My 68 Chevelle engine has a higher speed noise that occurs in any gear at about 2800 RPM. It sounds bad. It's a fairly loud whistling sound, that could possibly be the sound of metal. I'm trying to imagine if the timing chain is loose or worn and this is causing a constant ringing noise. Above 2900 the noise goes away, but the engine doesn't seem to feel as good... hard to describe. The engine is a 402 from a 72 Monte, has a medium crane cam, Holley 3310, hi-rise Weiand manifold. Otherwise, the engine runs great, starts great, idles well at 650, and generally feels smooth and has good torque.

I recently had the muncie transmission overhauled, and I'm wondering if it could be the tranny rather than the engine? I didn't really notice the noise until after the tranny was rebuilt.

Thanks

Sounds like your throw out bearing--Next time you hear the noise lay you foot lightly on clutch pedal. If noise stops you found the noise. Just adjust your clutch rod so that there is clearnace between your throw out bearing and the fingers on clutch plate.

How bout a vacuum leak?

I was thinking a leaking vacuum booster.

Well, it's not the throwout bearing, as I couldn't get the noise to change using the clutch. But a vacuum leak? Hmmmmmm.

If the vacuum booster's leaking, the only way I could determine that would be to plug the vacuum to the booster and see if it still whines. I'll do that ASAP. (and remember to brake early!)

I spent a lot of time at those RPMs today trying to get a handle on the source of the noise. It's VERY metallic sometimes, and if I creep up slow enough to the RPMs it sounds like it could be a super fast metallic rattle (very high pitch and very fast)which is what was making me think of the timing chain... like a chain being pulled fast through a metal opening, the individual clinks of the links are too close together and it seems like a consant metallic ringing tone. I also noticed two other things: It's a little different depending on whether I'm deccelerating or accelerating. Even the RPMs are a little different. And the other thing is that when deccelerating, as the ringing subsides, I can hear the motor "smoothing" out (or something). Almost like a clutch slipping, and then is slowly engaging. This naturally sounds like a clutch issue (which is why I thought it probably was the throwout bearing as jhow66 suggested). But I don't feel any slippage, it's more of a feeling that the engine is settling down, smoothing out. Sorry that's so mysterious. But if it was a vacuum leak, that might explain the vague feel of the engine improving.

ANY other ideas? Believe me I won't laugh.

As a follow-up. The noise is not coming from the brake booster either. It appears to be coming from the water pump (based on a really quick analysis last night).

I don't know if it's the belt or the pulley, or the fan or the internal water pump parts. I found out yesterday I could just rev the car up to about 3000 RPM in neutral and the noise would start. I checked pretty carefully around the engine compartment (with a stethoscope), and I'm pretty sure it's not coming from the valves or timing chain, etc. I only quickly touched the water pump near the pulley, and the noise seemed to be near there. I didn't want to get too close to that fan at 3K.

Anyone heard of a waterpump making a noise like this?

So here's my theory: The belt is loose.
The belt isn't *really* loose by my estimates (an old-timer don't need no belt tensioning thingamajiggy), but it could be tighter without hurting anything. SO if the fan was creating too much resistance at 2800 RPM, it would begin to slip under the belt, causing that awful screeching/ whistling sound. When I go faster, the sound stops, but that might be due to some kind of glazing or melting of the belt (the sides of the belt were very smooth). When I slow down, the "smoothing out" sound I heard, that I even said sounded like a clutch engaging, probably is the fan re-engaging with the spinning belt. This may also explain why the car seemed to run hotter at the higher speeds... if the waterpump is also running slower (on the same pulley). Alternatively, it could be the waterpump bearings starting to sieze, and causing similar symptoms.
So I'll tighten up the belt and grease the water pump/fan pulley bearings to see if that fixes the problem. I'll post back either way.

That was it!

Whistle/screech/ringing is gone.

I discovered my alternator bracket is (unfortunately) broken and that could very well have been part of the (loose belt) problem.

Woohoo, I'm back on the streets.