From what I've been reading, white smoke@high speeds=symptom of worn out piston rings.
But then, your bike is too young for that, ain't it?

While downshifting, make sure you've brought down the bike speed well enough for a particular gear. For example, imagine you're riding at about 60 km/h in 6th and you have to slow down for a speedbreaker. Don't immediately hold the clutch and press down 4 times to get to 2nd. That's when you get the loud thud sound. Anticipate the obstacle and start braking well in advance. Keep the bike in drive, moderately use the brakes, get it down to ~40, shift down once, let the bike go into drive again, slow down to ~30, shift down again and keep doing the same till you get to 2nd at a speed of ~10-15 km/h if the need arises. To sum it up, shift down at ~3k rpm. All this should be done in a very short time so this needs a bit of practice. While downshifting, use half-clutch. AFAIK doing that would eventually make your gears smoother.

Chain lube might have spluttered on the silencer pipe and might be evaporating once the pipe's thoroughly heated. I had an exact same incident. I could be wrong about your case though.
157 omg! That translates to ~142km/h taking into account 10% speedo error. Whoa man...

AFAIK NS gearbox is like that only, i mean upshifting is very smooth but as compared to that downshifting is not.... i have told this multiple times to SVC and they do some clutch adjustment and after that for few 100 kms it will be smooth but then again it regains its nature..... one more thing u need to shift very fast and at appropriate speeds for smoother shifts......thats my observation in 8K kms...

When asked same to the SVC they said it is like that only.... no bolt there....

Get a GoPro & show us..
The method you've stated above is 100% correct & it took me a while to get used to it too. But about using half clutch.. I had asked this to many people, SVC mechanics & testers. they all said use full clutch for downshifts ? Although naturally most people including me can only be able to pull half clutch cause it's tight & done so frequently during riding.

Started facing a problem since yesterday evening. This is with the rear disc making a sound like it is coming in contact with the pads at a particular point, indicating it is bent somehow. This problem already exists with the front disc. Now this is hampering in the free wheel movement which ultimately results in reduced mileage by minor margin and stress on engine and chain sprockets.

Is anybody else facing this issue?

Strangely though today morning when i went to drop off my son along with my wife as pillion the sound from the rear disc was loud. It is audible when the bike is at low speed but goes off as soon as it goes above 10kms, but when i went to office (no pillion) that sound wasn't audible except for a small khus - khus sound.

I will be going to the SVC either tomorrow or on sunday to get this rectified. Looks like problem of bent discs like a few had mentioned quiet some time back in this thread.

Could this also be a problem with the alloy wheels ??

it was not coming from the exhaust... It was coming from below the engine and it was all oily.... So either its engine oil leaking or chain lube.... But it cant be lube coz it started suddenly and then stopped when i came to a halt...and moreover i was running on an extreamely dry chain.... And my engine oil is 4300 kms old and still has enough life left... Its still reddish and quite thick....its motul 7100... Any idea if its the oil which is leaking from the clutch side packing or may be the front sprocket o-ring...? @aditya: i was running a dry chain and it cant be so much lube that my engine base with dripping with oil.... And it was quite scary at 157... The tacho wont move a single mm more...was stuck at around 10.7k rpm.... Took a long time after 150... @broken: u have a go-pro? i would love to tape it... anymore idea how a video can be taken?

I had this kind of experience when I was red-lining my bike to check for coolant leakage/radiator fan working. Was there any kind of oil on silencer?? Like the blacked engine oil that the SVC guys pour amply to lubricate?? I had such oil poured by SVC mechanic.

Just out of curiosity, how did you touch 157 dude? With 10% (assumed) speedo error, that is still > 140 kmph. Too high speeds for a naked.
How's the windblast at that speed?
And how many kms of traffic free stretch did you actually need to reach 157 kmph?

Hi

You can try one thing which works very well for me. While downshifting after u press the clutch lever, that moment blip the throttle a bit, and then downshift, you will get a very sweet click sound and no thud or kat kat shound.
Hope that helps !!

Yeah NS's clutch lever is tight. My left arm is probably just as strong as the right one now! I saw the half-clutch solution here on xbhp but don't know exactly when and in which thread. Also, use half-clutch only till the gears smoothen out over time. My gears were really hard before, had to use a lot of force to shift the gears up or down. Also I mostly ride wearing flip flops so I had lost some skin on my toe so riding wasn't too much fun. I began shifting using half clutch and after a few hundred kms, I could shift smoothly along with a nice click.
For those who feel shifting is hard, make sure the lever alignment is proper. Got mine aligned a little downwards and it helped me shift better (I have long legs ).

Check if the wheel alignment is proper. If yes, and you still get the sound, the disc is the culprit. Get it replaced under warranty.

Yeah, redlining in 6th on NS is hard. Btw, I remember you had mentioned earlier that you're running rich. Doesn't it mean that top speed would take a hit? Or did you make it lean again? When mine was rich I couldn't cross 142 km/h speedo indicated and after I made it a LITTLE leaner, I touched 152.

Yep, that's a good method too!

Btw Last time I was buying motul oil, the salesman kept arguing that mineral would help the bike run smoother than FS! He kept insisting I buy the mineral oil and when I refused he began abusing me! I told him to shut up, take my money and give me 300v! Looks like no one was buying his mineral oils! Btw, what is the drain interval for 300v?

Wish I had it lol.. it's just so expensive. Rs 30k+!! btw, taping your phone's vid camera to your forehead would be a good jugaad.. but you're gonna have to ride without a helmet then !.. hahaha..... okok that was a joke :P
See I had the exact same problem.. difference being that my bike had recovered from an accident. That khus khus sound is coming from your rear Disc Caliper (new costs about Rs 1800+).. I was told by the mechanic to live with it for a few days & the sound should go away on it's own. and it did.. or else I would've spent money on a new disc caliper unnecessarily. The sound used to get louder with speed & very less audible at low speeds. But it's gone now.

LOL! abusing for not agreeing with him ? like maa behan ki gaaliyan ?
He must've thought you know nothing about lubricants haha.

btw, I bought 2ltrs of Motul 5100 15w50 today Rs 460 per ltr.. Engine Oil filter Rs 74, O ring .. just cost me Rs 5 ? (Is it the right one?) Hopefully tomorrow I'll give my NS Motul oil atlast. Currently at about 2500kms.

What's that??? and for what??

Hi..
My bike hadd the very same problem which your bike has. This noise started after my bike completed some 200-300kms on the Odo. I spent almost entire month runniing to the seriver centre to get it sorted. First they thought it was the chain then they thought it was coming from the sprockets...everything was clened and lubricated but the sound didnt stop since the sound would magically disapper when i took the bike to the service centre. Finally i got irritated and had to complain to Bajaj regarding this and then i was called again to the service centre for this and luckily the sound came at theat time. It was then when they realised its the rear disk break which is the source of this sound. The caliper was opened then lubed...pads were cleaned using amry paper. Sound vanished only for about 10-15kms and it would reoccur at speeds below 10-15kmph...Again i had to visit the service station for this and then Trial and Error session started...they replaced the disk plate on visit 1....nothing happend....Visit 2 - Disk Pads Replaced...Result? Same noise still coming at those speeds...visit 3...Caliper assembly changed...result?? ...Visit 4- Service enginner was contacted in Pune and he suggested some solutions for this problem...so they opened the new Caliper once again...caliper pistons were cleaned and lubed generously..rear wheel spacer/bush whatever it is called was opened and lubed....Result...finally the noise stoped but still at times it comes again ocassionally. Overall it solved 99% of the problem.
My suggestion is get the claiper piston cleaned and lubed...pads cleaned by amry paper and also clean and lube the rear wheel spacer/.bush on the right where the disk is attahced to the wheel.

I hope this helps you and other who have been facing similar problem.

Its the rubber gasket for the oil filter cap.

Thanks Aditya. I will get this done for both the front and the rear. So from where can i get the alignment done from any car shop or are there separate shops for wheel alignment?

Thanks Broken87 & A@shIsh for your replies. I do feel that it could be a problem of the disc but the rear it suddenly cropped up, hence will also do the wheel alignment check.

BTW how much does wheel alignment for bikes cost?

Could it also a problem of the bearings? i normally clean the chain using Turpentine oil so may be some might have got into the bearings rendering the lubricant inside it a lil thin. what do you think?

Also another strange think i notice is that if there is a pillion the sound is more audible. Its like then the rear wheeltyre is under pressure it bents more making the loud noise, but when i am driving alone just a mild khus khus.