Bearing speed drop/whining noise on a 96kW Ibiza

Hello, dear Diesel Mechanic Forum,
Recently, I noticed that in my 96kW PD TDI Ibiza, occasionally, when I rev the engine while it's idling up to about 2500 RPM, the engine speed drops slowly, and the engine makes a slight 'whining' noise. Of course, as is often the case with showroom effects, it didn't do that at my dealer's. Does anyone else experience this problem? Could it possibly be related to the LMM?
Oh yeah, the car has only 1400 kilometers on it.

I would appreciate any response.

Best regards.
Timo.

Hello, it's probably not related to the LMM (likely mass flow meter), as it only provides the MSG (likely mass flow sensor) with the actual air mass. When you release the accelerator pedal, the engine control unit (ECU) is informed that no power is required, so the fuel injection amount is reduced and the idle speed is targeted.