Music app volume changes

Amongst other issues I'm having with the iOS 7 Music app, I've noticed that while I am playing music, the volume will abruptly increase.

I'm not sure if it's abnormally low then abruptly increases to "normal" or it's "normal" and increases to a higher volume. I think the former, as I am finding I have to turn my car radio higher than normal (up to volume 26 or 27 instead of 20).

Anyone else having volume issues? This has happened at least half a dozen times. It's the least annoying of the music app problems, but wondered if it's just me.

Thanks.