top end engine noise mainly between 1950 - 2300 RPM

[Blazer406]

First....my '96 has 326k miles.

Around 20k miles ago..... I began to notice a small amount of engine noise when the engine revs from 1950 or so until around 2300 RPM or so. It is quiet at idle and until that magic RPM. It is quiet past 2300...... just like you turned the switch off..... really wierd. It progressively gets worse starting again around 4000 RPM maybe.... It doesn't appear to be much difference loaded (in gear) or unloaded (park). It is much more noticable with the hood up and revving the motor by hand.

Any ideas?

Car doesn't smoke at all...... and has adequate power...... timing belt is due again.... was replaced last time around 230k......

[bob2]

what does the noise sound like? can you record it, and post a wave file?

[Blazer406]

Originally Posted by bob2

what does the noise sound like? can you record it, and post a wave file?

I had a piston one time in a SBC that had a cracked skirt that sounded similar.

The peculiar thing with this one is it is quiet like a 20k mile motor until that 1950 RPM.... and it gets quiet again once you go past that 2300 RPM or so..... just like you turned off a light.... it is wierd.

It does come back a little around 4k RPM and possibly progressively gets a little worse the higher you rev.... but it is hard to tell.... cause the engine is pretty loud anyway at that RPM.

The noise doesn't affect power noticably either....

At first I was thinking VVT, but I read.... it doesn't have VVT.

It is almost too loud to be top end.... but not solid enough to be bottom end noise.

It sounds like it is under the valve covers to me.

I'll see if I can shoot a quick video maybe....

[pmesfun]

Maybe stretched timing belt slapping the timing cover?


Noticed you have an 87 GN.