Strange noise from muffler

[M3!]

Started my car up this morning and heard a strange noise coming from the muffler. At first it sounded like something was stuck in the muffler, checked it out, was clean. Tried to inspect the bottom of the car but could not see anything unusual. The car continued to have a deep throaty growl. (hard to explain, too bad we cant add audio to the posts) After about 5 minutes the noise went away. Has anybody encountered this problem?

[Malcolm991]

Strange thing is that I had the same problem today when I was leaving work. The sound went away when I started to drive.

[sudz]

VERY WEIRD! I noticed the SAME thing this morning, it went away once i started driving/car warmed up.

Mine wasn't a steady "hum" it was more of a throaty pulse. pretty deep. At first i thought the car was running on 3 cylindars, but the engine light would have come on then... right?