iPhone4 tracks fast forwardingskippingstopping during iPod use

I have an iPhone 4, and use the iPod mode to listen to music while exercising. Today, after about 40 minutes of use, I started having issues. About halfway through song, the track started to skip, as though it was being fast-forwarded. I tried replaying the song, and the same thing occurred. Skipping to other tracks didnt work either. Sometimes the song would skip all the way to the end, other times only for a few seconds then end altogether. It happened toward the end of some songs, and barely a few seconds into others. While this was happening, I was also being interrupted by the Voice Command feature coming on automatically. This happened at least half a dozen times, but did not seem to be the cause of the skipping. Once I cancelled the Voice Command, the song would initially resume playing normally. I did have another app (solitaire while on the stationary bike!) running, but closing it did not fix the problem I have considered doing a backup and restore, but have not done so yet. I did have the Shake to Shuffle feature off, though I keep it propped up on the machine so the phone was not being jostled. I appreciate any insight and suggestions you might offer. Thanks!
iOS 4