iPad music fades in and out on iOS 5

When I am using the iPod app on my iPad 2 with iOS 5, the music periodically fades in and out randomly during playback. It happens during a song. That makes it impossible for me to use the iPod app and seems like a software issue.Today I notes that it happens if you're downloading songs in the background. When I am listening to music and downloading my purchases music from iCloud at the same time