ESP Light and strange motor sound

Hi,

I am having some strange problems with my A4 2.5TDI Quattro. Sometimes when I start car, in first few hundreds meters ESP Light turns on, and motor starts to sound different. It has crisper sound, like hood is open or w/o sound isolation. At that moment I am usually still on parking lot, driving slow and almost straight. Later, again without obvious reason it turns off and sound of motor is same again. Sometimes light's turns off few seconds later after motor get's usual sound.

It bothers me a lot, since I can't reproduce that behavior when I want and I guess that guys from garage will think that I am crazy when I try to explain.


Thanks,