On the advice of this board and others, I bought a second hand phase 90 on Gumtree for 50 quid. Great deal. However, today, I plug it in, and find that, while it works, it causes a whole lot of popping and crackle. It seems to distort chords if you play them to hard, and single notes seem t have a really nasty "popping attack, whenever you use a pick. Any ideas what the problem could be?