intermittent knocking/tapping sound

[bela77]

Hello,

I am sorry for not writing in English, but I don't speak much German. I apologize for this. I am writing to this forum in order to be able to resolve an issue with my RS4 which I have been fighting for a year now and spent a fortune on trying to fix it, however nothing is making a difference.
First of all the car has a standard AZR engine which first had an exhaust manifold crack and took out the passanger side turbo. Replaced both the manifolds and both of the turbos just to have a piece of mind.
One month later the engine started to make a knocking/clattering noise between 800-1800 rpm, the frequency of the sound is moving in parallel with rpm. After the engine is completely warm the sound is gone.
I immeadietly though that it is either hydraulic lifters or big end bearing so I took off the oil pan and inspected all of the bearings and none of them had any wear or damage, but since I had it open, I installed new OEM bearings. I've also opened up the valve cover and saw slight wear on the cams, so I also replaced all 4 cams and all 30 hydraulic lifters, put the car back together, started it and nothing has changed, the knocking is still there. Measured oil pressure and it is well over the minimum limit described in ELSA.

Of course I have checked everything else, alternator, A/C compressor, all parts of the timing belt, rollers and basically listened to the engine with a stethoscope for days trying to pinpoint the sound, without any success, and now I am out of ideas of what it could be. In the past one year I've also replaced my clutch, oil pump, flywheel and basically every bit of moving part in the engine, checked that all sensors are tight, etc, etc, etc.

I've ran different grades of oil (0w-30 <-> 15w50) in the meantime for testing if it has any affect on the sound, but nothing.
Compression check also came out good, so the rings are good. The car does not eat oil, water nothing and I've driven about 25-30k km since it first started to do this. People just tell me to drive it but it is so annoying and you never know when it is actually going to go boom. So if anyone has any idea please share it with me.

Here are two video clips i've taken, please listen to them. The sound also comes and goes intermittantly.

https://vimeo.com/112735485
https://vimeo.com/112735486

Danke!