Help - I bought my Crate 6 months ago second hand. A week later the speaker blew. New speaker fitted, but recently the limiter light keeps coming on and cutting off the sound. Whilst there is no sound the speaker is pulsating and popping and then it comes back on. Last gig it went completely and now doesn't work at all. I'm not pushing it hard - only 4 or 5 on the dial. Any ideas??