My M3 has had this fault a couple of times in the past week or so.
Only first thing in the morning tho' when really cold. All the radio stations on the idrive disappear leaving maybe just radio 1 and a local station. Trying to listen to either of them however is useless as they sound like the aerial has been unplugged.
Get in the car later on in the day and all is back to normal
radio station list has repopulated with 20-30 stations and radio becomes crystal clear again?
Has happened 2 or 3 times now but always rectifies itself. I used to run LED DRL's and these caused interference but have since removed them and popped the OEM bulbs back in so know it isn't those causing the problem.