Not sure if anyone on here uses the droid as a music player but I may have found a problem with the headphone jack. If you have the media volume all the way up it will distort the sound in the left speaker. I found this out cause I use the music player in my car and it only does it in the front left speaker. It does it on my headphones, only in the left ear. I took my droid back to verizon and they gave me a new one and it does the same thing. They said it may be a software problem. It also only tends to be a problem with hip hop/R&B, basically stuff that uses a lot of bass. Before someone says don't turn it up all the way, I only do it in the car so it comes through clearer. Also, it does not distort sound with volume all the way up when not using the headphone jack.
Sorry for the long post.