Knock, goes away when revved, WTF?

[h82crash]

89 i engine, just started a knocking sound toward the front exhaust side down low but goes away above 1500. Stethoscope on the block or head reveals no knocking sounds just valve clicking. My only guess is an exhaust leak but the gaskets are new(1000 mi), or something wrong with the A/C compressor pulley. Anyone experience this?

[e30loverSC]

Maybe throw out bearing

[jlevie]

It is easy enough to prove/disprove the A/C compressor as being the cause by removing its belt. If the noise is still present with the A/C belt off, check the harmonic balancer for signs of delamination or looseness.

[stumble_t]

also check the exhaust center support bracket. Mine made crazy knocking noise until I tightened it.

[calz4m]

This could be a sound from the clutch. Get in the car when its running and depress the clutch. See if it goes away. My track car does this.....sounds like knocking at idle.

[TrackjunkiE30]

Maybe throw out bearing

+1. My buddy's car had a similar sound and he said it was the throw out bearing.

[h82crash]

TKS for responses but the car is an auto. Haven't had time to check it out yet. My friend brought his e34 530 and I did the front brakes, spark plugs, K&N air filter, belts, coolant and oil change, and replaced both fog lights. I had no desire to work on my own stuff.