I've never had this before, but I've just (finally) tracked down a source of distortion in my home system. Turned it on one day and could hear distortion at even low volumes (23-25/100). Both speakers, all sources. Luckily I have quite a lot of gear so I could test various components out. Started off by unplugging speakers, and plugging another known set in (that was 100% working). Still have distortion. Cross off speakers (phew!). I have a amp/poweramp combo. So i disconnect the power amp and go straight from the amp. Still have distortion. On a hunch, I decided to plug amp straight into wall socket - bing, no distortion. Somehow, my "circuit protector" power board has had something borked in it, and it was making my setup sound terrible. Also going to check other devices on this circuit, to see if anything else capable of introducing noise. But anyway, not asking for help, just thought I'd post this up in case anyone else comes across an odd issue like this.