It is difficult to say what your problem is but if it has only appeared after the cam belt fix then it is a good chance it is related to that. You don't say what was replaced when the job was done but it is common procedure to replace the water pump and the relevant pulleys/tensioners when doing this and saves any hassle further down the line,one more thing worth considering is to remove the covers and double check the actual tension of the belt,too tight and they usually whine.
cdc, March 2016
