Radio/CD unintended muting
 

I have a 2001 MB s-430 with 8,000 miles. We also have the voice command telephone. There is a strange problem with the radio and CD. A few times a week the radio or CD mutes for about five or ten seconde and then resumes. I tried all the phone connections and nothing seemed wrong. If playing a CD the timer stops and it mutes exactly as if a telephone call was comming in. Went to the dealer who made a software upgrade and turned off some option. It's seems to be the same. Anybody know of any solution or suggestion to the dealer?
Thanks,
Howard

Might want to re-post this in the Car Audio section:)