a/c control noise even when the car is turned off

[tranq72]

I have an horribile (tick-tick) fan noise coming from the A/C control panel of my '05 X5 E53.
The noise begin when I unlock the car and open the door and never ends
(actually I think it ends after some minutes once the car is locked again)
In another forum I've been told it may be the inside temperature sensor fan which is dirty and needs to be cleaned or replaced.
Does anybody know how to unscrew the panel and reach such a fan ?
If it is simple DIY task I'de like to do it myself (unsure about warranty for such parts)
Thanks in advance!
Nico.