This happened to me yesterday. I did not confirm that it was the music but what you describe is exactly what was occurring on my phone. The phone keeps trying to download music and for some reason it is unable to. Its like the phone can download the file but then doesn't move it from the download temp folder into the music library.
When I plugged my phone in to my computer, iTunes showed 37 GB of other and I can only imagine was failed attempts to download music files. I did a clean install again this time I was careful about selecting what music to download and it appears to be ok for now.
Worst part of it is that I had enabled the cellular data download for store items and it ate through my data cap in an afternoon. By the time I found out about it I had received the 90% of data warning.
Should this happen again is there anyway to clear the wasted "other" data or the downloaded temp files out?