1997 Altima noise around 2,700 and 3,000 rpm

Hi to all:

I just purchase a 1997 Nissan Altima with about 83,000 miles on it. Maintainence records, clean oil, etc. I noticed when driving at about 2,700 to 3,000 rpm I hear what sounds to be a rattle...They type that may come from a shield or guard. The frequency of the rattle stays constant as you rev the engine past

2,700 rpm. I've also listened under the hood, revving the engine by hand, and it seems as though it's coming from under the engine. I must say though, that it is more noticeable inside the car than while listening under the hood. The exhaust system was recently replaced. When listening inside the car, it seems as though it's coming from under the engine. It also sounds like it may be a bearing. Does the idler wheel sometimes produce this noise? Could a frayed serpentine belt produce this sound? (Or whatever the belt is that rides against the idler pulley)

I stopped in my driveway, revved the engine up to the 2,700 rpm point and hear the rattle. I guess I can rule out the transmission.

Any ideas? The guy that sold it to me just had the plugs changed, changed the oil with Mobil 1 synthetic. Other than the rattle, the engine has lots of power, and I cannot see anything obvious-> I'm not a mechanic though :(

Thanks for the help. I hope that it's nothing serious.

Art

I also have a '97 altima, mine has 130k miles on it. I had the same problem about a year and a half ago. Only my rattle was at low speeds. Turned out to be the heat shields, had them removed, no problem since.

Thanks for the return post. I think they are fine now...Haven't heard the rattle in a while. Seems the exhaust was put on just before I purchased it.

Art

If you hear a rattle at idle coming from the passenger side of the engine, see Nissan's Technical Service Bulletin NTB98-055a dated 15 November 1998 which addresses timing chain noise caused by the upper and lower timing chain guides. It's a $750 to $1100 job depending on what else needs to be replaced.