Ideas on C2 underhood noise during warmup - help!

[Timothy B.]

I have been experiencing a noise under the hood that I haven't been able to figure out. My 67 327 vert makes a strange underhood noise during initial warmup and acceleration. Once the car is driven only a few miles the noise dissipates. The sound is hard to describe, but is similar to a mid frequency vibration or maybe even an exhaust leak. The noise appears when the car is not yet warmed up, regardless of actual ambient temps. After a short distance, it goes away.

I recently replaced the exhaust pipes front and rear, new exhaust manifold gaskets, new pipe to manifold donuts, etc. I had noticed the noise prior to the pipe replacement and hoped that new parts would take care of it. I used no sealer between the front and rear pipes.

Anyone experienced a noise similar to this and if so what turned out to be the cause? Can the pipe joint between the front and rear pipes make such a noise during warmup only?

[Mike Geary]

Re: Ideas on C2 underhood noise during warmup - he

Have you checked the heat riser? It can make some pretty weird noises when cold if it's cracked.

[Timothy B.]

Re: Ideas on C2 underhood noise during warmup - he

When I replaced my exhaust pipes, I removed the heat riser and installed the blank heat riser spacer from the FI cars. So, I know that's not the problem. Thanks for the suggestion however.

[Wayne P.]

Re: Ideas on C2 underhood noise during warmup - he

Sometimes bearing noises, like the alternator, can do this before they completely fail.

[Gerard F.]

Re: Ideas on C2 underhood noise during warmup - he

Could it be your belts slipping? Just a thought.

Jerry Fuccillo
#42179

[Rob A.]

Re: Ideas on C2 underhood noise during warmup - he

Tim,

Next time you start the engine up cold, putone end of a rubber hose on the alternator and the other against your ear. If that's the noise source, you'll hear it magnified. The bearings will sound worse during warmup, if they are going bad.