Ratcheting noise at end of rev

[Optllizer]

Its been awhile since I posted, but I am officially out of ideas for my 2006 BMW X5 3.0i with 224k. Currently, its make a weird rapid ratchet noise at the end of a rev while in park and while cruising but not all the time.

-Car needs to be fully warm.
-Car has to have been driven for more than 5 mins and reach rpm above 2k.
-Car's cold start has no extra noise and not even the standard 2-3 second ticking either.

You can hear it while letting go of the gas and cruising with barrier echo. You can also hear it while decelerating at a light or stop sign. The noise stops completely after idling for about 5 mins and couple revs. id need to drive it above 2k rpm again for couple mins to make it come back.

Whats interesting is, I do not feel it in the car or while accelerating. If window is up and music playing, car is driving very smooth without issues.

DISA Valve was recently replaced but its the noise isnt near that. I thought it was the VANOS but I had someone rev and i put my hand on it and no extra vibration with the noise. Regardless, it could be the VANOS still, just seems unlikely.

I took a look inside the bell housing port and nothing from a quick glace. its spinning fine and when someone rev with the noise, it didn't look abnormal.

Noise "seems" like its inside the oil pan but it could be echoing from somewhere else.

I did an oil change today with Castrol 5w-40 and the noise didn't change frequency or volume. I did it at 5k. No plastic or noticeable metal in the oil, just standard black color.

Here is the clip.
https://jumpshare.com/s/q7nt2CE2RiM5GGQIhSgO

[80stech]

maybe cracked fan blade? cracked flex plate? maybe have a look at the oil filter if it sounds internal.

[X5chemist]

I've heard it before on vehicles. Especially high milage vehicles. A bad belt tensioner. If yours is hydraulic, check for oil residue.

[Effduration]

Can you have someone else reproduce it while you fish around with a mechanic's stethoscope - cheap on amazon?

[80stech]

A piece of garden hose or something similar with one end stuck in your ear might be even better since you can pick up the noise as it's going through the air as well.

[Optllizer]

I purchased a Mechanic Stethoscope and its coming today or tomorrow.

I had a look at the hydraulic belt tensioner and the noise is not from that area. I forgot to specify the side of the engine with the noise. Seems to be on the passager side and lower down the engine.

If the flex disc was cracked or loose, wouldnt i feel it inside the car and while driving the car?

[X5chemist]

The A/C compressor is down low on the right side. How old is the compressor belt tensioner?

[80stech]

In this case a 3 ft. piece of garden hose, heater hose or something like that would probably work better than the stethoscope. Taking the belts off might help eliminate some things but probably wouldn't need to if you use the hose.

[Optllizer]

I made a discovery about the noise. I put a screw driver on the cats and had someone rev. As the noise happens, i felt a ton of vibrations that were with the noise while the touching the cats.

My question now, what would be inside the cats that would need engine warm and driven a decent amount for it to become loose and make a rapid rachet noise near end of a rev but disappears after 2 mins of idle?

[80stech]

If it's a consistent ratcheting it might be in the exhaust valve train and not cats. Use the hose trick to find where it's coming from. Any kind of loose baffle in the cats will change with temp changes if that's what it is.