After reading the very first line i could make out that you were in wrong hands.
""""""""""""""""""""so i checked with one of mechanic he said it my be a timer belt problem so he tried to adjust sumthing on the timer.""""""""""""""""""
Timing belt adjustment IS THE LAST THING TO BE DONE. And for fooling people few big head mechanic use that tactics exactly and then play around with car and keep making money.
Dump that mechanic at first, PLEASE. And go to some good garage like dynatrade, technical garage, AAA etc to get the proper fix of this isse. There is nothing much to clean the silencer, its advisable to change it as you will be changing only mufler and not whole silencer, which would cost less than 500.
Timing belt is due to change at 100k so check with ur friend if he has changed or not. May be coz of timing belt is due to change then adjusting wont help but instead you have to change it.
Good luck.