N54 Engine Clank *Not rod bearing related*

[jeddo45]

I got an issue that I, nor my mechanic can't put our fingers on. I'll explain this as detailed as possible hoping that someone else has had a similar issue.

At about 2k RPMs, there is a noticeable slapping/ clank coming from the engine. It also happens on neutral so it's not anything driveline related.

The issue is mainly from 2k to 4k RPMs only when I'm hitting the gas. From idle to about 2k, no clanks or slapping noise. But from 2k to 4k RPMs, its a very loud definitive clanking/ slapping. The noise coincides with the speed of RPMs. When I let go of the gas and the engine comes to an idle, the noise doesn't happen at all no matter where I'm revving the engine.

My timing chain and guides have been replaced but the noise is still there. Since the noise happens only within that RPM range, we don't think it's rod bearing or piston related.

I'm going to try and upload a video and see if you all could hear it. In the meantime, any thoughts? The car runs great still. No noticeable performance drop or limp mode. I'm baffled.

Any suggestions?

https://photos.app.goo.gl/dJeo7zEerPUxM5hR8

[Tejas1836]

Did you own a cat?

[GuidoK]

My first guess would be the vibration damper. Or maybe some weird resonance from a belt tensioner or such.
But a clacking sound like that (non intermittent on a stationairy car) shouldn't be too difficult to locate?

If it comes from within the engine (or within a stationairy part), use an engine stethoscope. A cheap and really handy tool.

[10"]

I mean at that range from about 2000-2500 is when the N54 twin turbos really start going up to about 4000+ is their peak range—so without knowing much more I’d wonder about the turbos. It’s nothing like the famous wastegate rattle?

[XutvJet]

That is absolutely rod knock and the rpm range you're noting is the common rpm range that it tends to be most audible. I'd find another mechanic if they couldn't tell that was rod knock within one engine rev.

[chris719]

I have to agree with XutvJet that it does sound like rod knock.

[tracer bullet]

I've heard sticky (open) injectors sound like rod knock.

[meadowsdb]

Rod Knock. Keep your foot off it before you have a hole in the block.

[TheMidnightNarwhal]

Unfortunately does sound like rod knock. That said, I would try to run the car with the serpentine belt removed just to rule out any accessories. I've read in the past someone who thought he had rod knock on his N54 but it ended up being the AC compressor. Good thing to try and rule out (unless your mechanic already did it).