Itunes songs ending prematurely and fading out at parts?

I've had issues with songs ending too soon (anywhere from 2 minutes to 20 seconds of silence instead of music) and I can't remember how I fixed them. Its happening again, but now some parts of songs are fading out, and I'm not sure why. I haven't changed the settings, and it seems to only happen on some songs. It happens both on my iphone and my itunes, both of which are up to date. This seems to be happening only with purchased songs. Any ideas on how to fix this or what could be causing it?