iPods are great aren't they? Well not if you are using one and have your mobile phone near you.
Try this on for size. Pick a nice loud AC/DC track (or similar) on your iPod, and then place the mobile phone near it. Get someone to ring you or move suffuciently for the phone to search out another cell. When the volume jumps to full on your iPod, it doesn't half make you jump.
I tried this a few times just to see if that was the cause and yes, I can assure all, the phone interferes with the iPod!
So they must interfere with other stuff.