Hi guys,

I’m getting a random clicking/knocking noise from the bottom of the engine area on a 2015 C7 Z51 (8L90).

• Noise is not perfectly rhythmic, follows engine speed but doesn’t happen every revolution
• Starts about 1–2 minutes after cold start
• Most noticeable at idle / low RPM, mostly disappears above ~2500–3000 RPM
• Much louder from underneath, barely audible from the top
• Oil pressure is normal
• Oil filter is clean (no significant metal)
• Recently had torque tube service (bearings/couplers)

I checked with a stethoscope and the sound seems strongest along the oil pan area rather than the top end or sides of the block.
I also opened the front bell housing access cover as mentioned here, but I couldn't 't tell that the noise was coming directly from the hole. It seemed more like center of the oil pan.

Attaching a video below.

Could this be flexplate, coupler, or something else?
Any input appreciated.

Thanks!

You Tube

 

Welcome to the Forums. I can hear that thapping sound, it is nonconsistant. Almost sounds as if something is loose and flying around in the flywheel area. Was that noise there before the torque tube service? What's the condition of the starter? (bendix). I don't think it's coming from inside the engine, but it does sound like it has solid lifters. I would start with pulling the inspection cover off the bottom of the bellhousing and do some inspecting, checking bolt torque and something loose and flying around and go from there.

 

I removed the serpentine belt tensioner, but the knocking from the oil pan area is still there.



I also checked the torque of the flexplate bolts, and they seem properly tightened.

I tried to look for signs of loose rivets on the flexplate, but through the access hole I didn’t see anything suspicious.

It’s also hard to pinpoint the source of the noise, as it seems to resonate throughout the entire oil pan.

 

A stethoscope might be helpful. Its hard to imagine that kind of noise coming from inside the oil pan. Though not impossible. If you could when the oil pan is cooler engine running, with gloves on place your hands on each side of the oil pan and see if you can feel something that matches the noise.

 

There is a possibility the noise is traveling up the torqure tube from the rear of the car. you might try listening to the rear area also.

 

I agree with Thomas and the use of a stethoscope. Probably the best to get it up on a rack where you can easily access all the possible points that the noise may be emanating from.

 

I tried using a stethoscope, but the noise seems to travel through the oil pan, so it’s hard to pinpoint - it sounds like it’s everywhere along the crankshaft area.

At this point I’m leaning toward the flexplate. My car has the early riveted design of flexplate ('14-'15), and there’s a GM service bulletin about noise from that setup.

I did check the oil filter and didn’t find any meaningful metal, which makes internal engine damage (rod/main bearings) less likely.

The only thing throwing me off is that the sound doesn’t exactly match videos I’ve found online and it's not clearly coming from bell housing service hole.

Still open to other ideas.

 

You could drop the pan and see if the windage tray is involved. Can't really think how it could be tho.

 

Was this noise there before the torque Service? You could take it back to who did the torque tube service and relate the noise to that. I worked on a 79 Corvette once that had a tapping noise, this other guy that was helping said it was a valve rocker. We had a debate, it was loud like a rocker. The cause was a bad spark plug wire.

 

I don’t know. The torque tube was serviced by the previous owner.

I took the car to Orange County Transmissions, the shop that performed the service. Their work is still under warranty. The owner listened for a while and said he has poor hearing.

They then claimed it’s not their responsibility, said it’s engine knock, and refused to even put the car on a lift to help locate the source of the noise.

Today I performed a cylinder cut test. I disconnected each coil with the engine running, and the knocking remained unchanged. If it were piston knock, the sound should have changed.