I have a 2000M with 80K on it. I had the rattling sound that I could not pinpoint. I notice it when you are in gear and off the gas cruising and not on neutral. It turns out that the flex disc was cracked and the center bearing was also bad and one of the bolts was also stripped out when the clutch was replaced a while back (done by dealer in 03).

Noise is now gone and car back to normal. I have had this issue for nearly 3 yrs and had never imagined that this was the case.

The air intake rubber should also be checked as it caused a lot of rough idling.