I have recently discovered a subtle clicking radio interference type sound on the clean channel of my JVM410H, when switching to the crunch channel the noise disappears. I had the amplifier serviced just over a year ago by Marshall and they replaced the power amp valves. The preamp valves haven't ever been changed since the the amp was purchased in 2009, ex demo. Marshall said they didn't need replacing when I had the amplifier serviced. The amplifier hasn't had a huge amount of use but it's hard to gauge exactly how much. I am guessing it could be a preamp valve. Any ideas?