Weird knocking noise??

[shr3ddymurphy]

Anybody no what this noise might be?
Thought it was the catalytic converter hitting the subframe, then once it was on the rack mechanic showed me a bad flex pipe on the the cat, so we decided to switch out the cat altogether. Just picked up the car and the noise is still there, but then it goes away once the car warms up.

Motor is mildly cammed LS3. I thought maybe motor was hitting something but my mexhanic said mounts are good so I’m out of ideas…

See video
https://youtu.be/wQhlogEvGbg?si=TwrDS4Qc39S6GlLI

[elc32955]

Hmmm... this is a weird one that I've not heard one like before. If it goes away after warm-up maybe it's a component slightly loose when cold - but heat soak causes expansion & snugging. You might need a guy with a stethoscope or a sensitive monitoring mike that can move it around quickly whilst the car's warming up to try to localize the rattle.

Good luck
Eric

[shr3ddymurphy]

UPDATE: Bad motor mounts ended up being the cause of the knocking noise. Got them replaced and now PPV is riding great with no knocking or rattling.