1998c280estate

Hi all. Here's a weird one. (I've searched the forum but can't find another example).

Every time I turn on the ignition to start the car (1998 C280 Estate, owned from new), there's a loud buzzing noise coming from the cluster of interior light switches on the roof/headlining. This has been going on for some months - I used to think it was just the heater fan, but now I see it's not. It's not noticable when the engine is running, so it may stop (unlikely). More likely it's still buzzing but inaudible over the sound of the engine. All the switches and lights work. There's no sliding roof.

Any ideas what it is (I've ruled out bees)? Hope it's not an electrical switch buzzing itself into a fire... Any suggested fixes?

I see there's a small plastic grille up there, just in front of the mirror - what's that for? Any moving parts in there?

Also, could this be linked to the tailgate interior light mysteriously coming on (and draining the battery) some weeks ago? Since then I've turned off the automatic interior lights coming on when the doors open, until I've checked the tailgate switch.

How do I prise the switch cluster off the headlining without damaging anything? (I broke a door handle cover getting it off to change the door capping, so am now very wary about how to prise plastic fittings apart without breaking them).

Many thanks!
Cheers,
John

1998c280estate

I can't believe I'm the only one here to have had this?
Anyway, if any of you are interested, another forum has explained that the buzzing is coming from a tiny fan in an HVAC sensor which is located within the roof light/switch cluster, and which blows air across the sensor to register the cabin temperature. It can be cleaned (usually unsuccessfully) or simply unplugged and replaced. Unfortunately, it's very expensive in the UK (£68/$100!!!), but apparently entire light/switch clusters come up on ebay. In the meantime, I'll just put up with it.
Cheers,
John