Florian,
There's boomy bass in a lot of recordings, especially pop or electronica. They're mixed and eq'd that way, so they sound good on dance floors and fm radios. Don't fret one or two songs. Find some naturally uncompressed recordings, like Mapleshade, or the RCA Living Stereo SACD's or something, and listen on those. If it's still boomy, then you know something. For this song (mp3 sounds boomy anyway) move on past it.
That being said, your RM-30's will continue to be a bit stiff until they break in, as all of us have been telling you. Just settle them into that room, get a glass of wine, get rid of the steering wheel and the coffee table doiley and you're fine!
And buy some floor mats!
Ted