weird sound - slk 230

[HBKHBK]

I am brand new mercedes benz owner and have the slk 230.

So I am wondering if you guys can help me out with what I experience and hear.

When I drive through a parking lot around stores etc...when I relieve my foot from the gas I hear for maybe 1-2 second a sound,like a sound from a belt or from the transmission.
I always hear it when I only drive very slow like at parking lots to find a spot and relieve my foot from the gas,then I hear a little sound,it is like tiny, 1-2 second sound like ratteling or something,hard to describe...i mean i hear it cause I pay attention...the sound is very low and u hear it when u pay attention and it does NOT happen when I drive faster than 30 and relieve my foot from the gas. It only happens at a very slow speed and only when I get off the gas and it last for 1 second...

Is that not normal? Just wondering... I mean everything else is fine and the inspection was clear as well

[blas0827]

yeap normal its the supercharger