Irregular subtle knock sound

[sibhusz06]

I just started noticing what I can best describe as a subtle knock that is not perfectly tied to engine rotation. Basically at idle or 600 rpms, I hear what I describe as a knock knock..pause knock knock knock knock...pause knock.. it is not perfectly rhythmic relative to engine speed, rather seems like it comes and goes..

Its very subtle and I can't capture audio but only audible at 650 rpms. If I rev to 800 rpms, it goes away completely and it does not follow engine speed any higher in revs. Ive tried to isolate it and it seems to be coming from the front of the engine around the alternator/ belt drive area but I can't tell if the pulleys are causing this or perhaps its coming from the engine itself.

Any ideas, thanks!..

[titleiststud]

I have noticed something similar in my car only when the a/c is on. Haven't cared enough to try to figure it out yet though. Interested to see what you find out.

[Helmsman]

Plenty data incl videos on this guys and have (fortunately) not yet any personal experience, but from all the data shown the rod shell typically start to knock on the door between 2000-3000 rmp, assumingly where the "resonans" takes off. Knock "only" around idle I haven't seen is related to RB's, but there is a first time for everything I guess… Also as you can hear in the sillions of vid's the RB knock is pretty loud and typically can't be taken for anything else.

[anerbe]

Originally Posted by sibhusz06

I just started noticing what I can best describe as a subtle knock that is not perfectly tied to engine rotation. Basically at idle or 600 rpms, I hear what I describe as a knock knock..pause knock knock knock knock...pause knock.. it is not perfectly rhythmic relative to engine speed, rather seems like it comes and goes..

Its very subtle and I can't capture audio but only audible at 650 rpms. If I rev to 800 rpms, it goes away completely and it does not follow engine speed any higher in revs. Ive tried to isolate it and it seems to be coming from the front of the engine around the alternator/ belt drive area but I can't tell if the pulleys are causing this or perhaps its coming from the engine itself.

Any ideas, thanks!..

flywheel chatter?

[titleiststud]

Originally Posted by anerbe

flywheel chatter?

After reading a lot of posts, etc. about it, that's what I determined mine to be. It only does it periodically, so I'm not too concerned at this point.

[sibhusz06]

In my case I have a DCT and am unsure if its flywheel chatter. Ive just decided to remove the belts and see if the noise goes away as this will hopefully isolate the issue to either engine or accessory/pulley.

[Solo_M_Tech]

Motor mounts being worn can cause the oil pan to tap the chassis reinforcement plate. I've seen it twice. Creates a very subtle, irregular knock.