Engine Grinding Sound - 91 300E

[gmercoleza]

Actually a couple strange sounds have occurred, maybe they're not related.

First, I started hearing a loud howling/whistling sound. It was extremely loud and would occur between 1750 and 2000 RPM. Very strange. Looked under the hood, nothing is out of place. That stopped after about a day.

Secondly, just last night I started getting what can only be described as a loud "grinding" noise from the engine area. It is definitely RPM dependent and is most noticeable with the windows down next to a curb. Sounds like a metallic scraping noise which increases as the engine is revved. I haven't looked under the hood yet; perhaps someone has suggestions as to what to look for.

I don't suspect the engine - it's in top shape. And I know a grinding noise like this would kill the engine in about 5 seconds.

Belt tensioner and water pump are new. I don't think A/C clutch is the culprit, as the noise doesn't go away with the compressor engaged. What else can make such a loud scraping metal noise? Alternator? Air pump (does my car even have one)? Transmission shaft? The noise occurs whether in P, N, or D.

Any ideas anyone?

Thanks!