BlackCar

I can also confirm the buzzing sound in a C4 for 20 or 30 seconds at startup is the brake booster in the trunk. Mine has made the noise for the 8 years I've owned it. If it stops doing that at startup it would be time to worry. I'm told this is expensive to replace.

Gweedo

Thanks guys! I knew nothing was wrong, I just wondered what they were.

I think I should get some RSRs though so I'm not distracted by any of those noises again

sidned

I put some Supercups on and the buzzing sound disappeared. Can't hear the radio now either or the mobile (cell) ringing!