Engine noise at 1000 rpm

[Divergent]

My 97 Camry makes a rattling noise from the engine whenever it hovers around 1000 rpm. Mostly this is right after it starts, and then once it warms up and starts dropping, the noise goes away. If I give it just a little bit of gas to bring it back up to 1000, the noise comes back again, but goes away again immediately after it passes 1000. What am I dealing with and is it anything I should be worried about? Thanks so much.

[earthmike]

Sounds like it may be a resonance frequency of something in the car. In other words, when the engine is at 1k rpm, something else decides to vibrate in harmony at 1k Hz, making the sound.

If you find what's making the sound, you can try to dampen it or add/shave off some mass (should decrease/increase resonance frequency).

generally,
natural frequency = sqrt(springiness/mass)

I had an engineering vibrations class in college but haven't used it much since so I don't know exactly how it may apply to getting rid of such things in cars.

--Mike

[Divergent]

Thanks, I'll try to test that out. A mechanic that I took it to said that it might be either the water pump or the timing belt tensioner. Any thoughts on that?

[earthmike]

I can't really help with specifics because I don't know how to diagnose cars.

<shrug> Have a friend revv the car with the hood open, see if you can pinpoint the location of the sound. That's safe to do, right?

--Mike

[87Camry5Speed]

^^ with trans in park (stick=neutral) and parking brake engaged, i dont see why not

Try and look for a mechanics' stethoscope, works like a doctors' stethoscope only for cars and not people. Supposedly you can hear noise inside the motor a little better.