[Sephx1]

There are times when the Bose system sounds good and the door speakers are pounding out strong bass, then other times when it doesn’t. This happens when I’m listening to the same source, which seems to be best when using my iTunes playlist. Could I have an amplifier going out?

[DarkKnyte]

Isolate the sound to a single front speaker using balance/fade when it is happening and listen for a distinct change in the audio quality. If it's the same song, same speaker, less bass then there could be a problem with your amplifier or the speaker itself.