also i've thought of installing an open chain cover...
for that i'll probably need an o-ring chain
any guess on the cost of the O-ring chain and open chain cover??
plz do suggest which bike's open chain cover will be a direct fit for my pulsar150..

Try putting one one cover at a time first the upper cover , go for a drive & check for any noise. then put the lower cover & remove the upper cover & check for noise whether it is present/ absent/increased or decreased . Im sure that by doing this you will be able to locate the source of the sound.Also check the rear tyre for any signs of abrasions.Hope this helps

Finally got hold of the problem!!!
i loosened(not removed) all four screws of the chain guard and pushed the chain guard towards the engine from rear end of the chain guard
and simultaneously tightened the screws
and the problem vanished!!!!
Now there's no sound at any speed
i would like to thank everyone for their help and concern

and i would also like to know that is there a certain direction of rotation of a chain??
i opened my chain for cleaning purposes and forgot in which direction it was ??:P

[Pulsar 150]How much should be the clearance between the Swingarm and the Chain?
My chain slack is under limits but it scraps against the swingarm near the Engine Sprocket.
I get khat-khat-khat sound when i change gears OR when im braking.the noise disappears if i press clutch while braking.
my shocks are at level 1(one stiffer than default-level 0).At first i thought the sound was from the case so i removed it and made the above observation.
I had changed my chain set in March this year.

hi buddy,

I'm facing the same problem, whereas my chain is rubbing against the chain guard near the engine sprocket and the chaain guard gets bend. also i tried to tighten the chain but still their is horizontal movement in the chain and not vertical which leads to the chain rubbing on the inner part of the chain guard. The chain guard in my situation is not rubbing against the tyre or any place else but still the noise continues. The noise is not audible after removing the chain guard. One thing i observed was the small sprocket near the engine wobbles a little and the engine shaft on which the sprocket sits also has a horizantal play. but the service center mechanic confirmed it to be OK. I also tried replacing the drum rubber and the chain lock but to no success..after i remove the upper part of the chain cover and test ride the bike the noise is audible at speed of 60kmph as the chain is rubbing inside the chain cover near the small window kept open to check chain play... Then i removed the lower cover and tried with the upper cover and the noise was there at speed of 50kmph and the chain was rubbing against the chain cover near the engine sprocket which caused the chain cover to bend a little....the chain cover im using is a new one. ...the mechanic also tired to hammer the bracket on which the chain cover seats by pushing it a little more towards the wheel but that was of no use, also i tried to flip the chain and also the engine sprocket but that did not help ....it worked for you by pushing the chain cover towards the engine side from the back end but for me i can't push it in anymore as the brackets wont allow me... Im stuck and cant figure a way out...probabaly ill try flipping the rear sprocket if that helps or else if it does not will try to replace the engine sprocket and then is issue still not resolved will try to replace the rear sprocket also....just as an FYI both the sprockets of my bike are in crisp condition even though i have clocked 55000 kms on her.....If nothing works i will probably change the chain cover and go for open chain cover like the pulsar220 or pulsar135... ..

well since you completed all the checks including rubber damper and chain link lock
i don't think there is any other problem else than chain rubbing on the chain guard
as you mentioned the cause to be horizontal play in the drive shaft
this might have occurred due to either too much tight chain or frequent overloading such as tripling,burnouts may also cause the drive shaft to bend.
well 55000 seems a big number but since you mentioned the sprockets were doing fine then it can be ignored.

in my opinion you should first correct the horizontal play in the drive shaft-either the shaft is bend or the bearings have worn out.
if this tends to be too much costly the simply resort to pulsar 180 open chain set which will be a slight over gear of the current setup but i hope you will appreciate the drop in rpm for the respective speeds.

i also suggest you to put on an open chain cover this is the cheapest of all the above methods but you will have to take care of the chain more frequently as the stock chain is a simple chain(without O-rings).