Popping Noise behind rear view mirror C240

[bonithol]

Hi. Can anyone help. My 2001 C240 makes a loud popping noise which appears to come from behind the rear view mirror. It is about 3 sec intervals and lasts for about 30 secs after starting the car. Any ideas?

 

[yachtman]

It might be from a microphone for the phone, if fitted. As powered up from ignition, you get the noise.
I have a similar effect on a truck at work.

 

[bonithol]

Thanks, Excellent, it does have Merc hands free even though I don't use it.