2001 Pontiac Grand Prix car making noises

Noises problem
2001 Pontiac Grand Prix 6 cyl Automatic 97,000 miles

My car has been making some noises for the past few months and when I take it to my mechanic, they can't seem to hear anything when they have it and tell me they didn't hear anything out of the ordinary. It is hard to describe, but sounds kind of rattle-like, or tapping. I also have a pinging noise. I was told in March of 09 that I needed my EGR valve replaced, but since then when they put it on the computer it doesn't detect anything about the EGR valve. It showed last week, though, that I needed a new oxygen sensor because mine wasn't working right, and I had that replaced.