my 1999 3100 53K Miles has a knock that is not in sync with the engine rotation, and speeds up from idle to about 2000 rpm, then it dissapears when accelerated further. At all speeds it is not in sync with engine rotation. It also is not always there. IT will be there for 30 minutes then gone for days. I have pretty much ruled out a rod knock being it comes and goes and is not always there, and is out of sync with the engine ( much much slower than the rotation of the engine. If I could guess, I would say 1 knock per 5 revolutions give or take a few.

can you take a vid or a recording of the noise in question?

you sure its a "knock" or a rattle of some sorts?

its no rattle. Unfortunately, I have nothing that I can get audio with.

Its more noticeable at idle than any other time. High rpms its gone completely.





Oh how I miss my Bonneville, I hate this olds, strange knocks, piston slap and all!!!!

well the knock is again gone. I'm sure it will be back. I almost think the knock sensor isn't working right? Who Knows?