I have a recurring problem with my pod HD 500. I've set up my resets and they sound like I want them to. Good sounds but after playing for a while the sound degrades and becomes thin and fizzy and quite nasty. Occasionally they come back but it then happens again. Any ideas? Really frustrating and don't want to have to replace the pod unless I have to. Not sure if it's a software issue or faulty unit. Bought it second hand so no warranty. I live in the UK.