ell in my case as I mentioned the culprit was timing chain. The 1st mechanic I went to did his "Jughaar" and tightened the chain but eventually the problem came back. So after few months I had to replace the adjuster "tension-er" and timing chain. The tensioner cost Rs. 3000 and timing chain Rs. 3300.
For timing chain, side cover and tapper cover needs to be opened and is avt 2-3 hours job, while tenioner can be replaced easily.