M52Cat

I just had new plugs, coils and wires put into my car and when i finally got it back i noticed a couple wierd noises. The first is the one that bothers me most, as i accelerate a high pitched rattle comes from under the car (not sure exactly where but sounds like its around the cat), the mechanic said it was excess build up in the exhaust from the bad plugs and it will blow out in a few days but it has already been over a week and nothing has changed.
The second noise sounds almost like a synchronized clicking coming from the engine its not very loud but im a perfectionist so it bothers me lol. Any help would be great cause i'm really stumped on this one. Thanks, Mark

M52Cat

anyone?? could i have burnt my catalytic converter?