i got my cats cut off today but i still have my stock muffler i plan to get rid of it but there is this sort of leaking sound like exaust is comming fromt the right side of the car so i took it back and they welded it some more but then it still makes the noise could it be cause its a stock muffler??

 

If it is a fluttering sound when you get off the gas, that would be an exhust leak. Look for the soot to find it.