I bought a new Shuttle 9.0 in May. Very quickly, (first gig, actually) I started hearing some noise in the amp. GB helped me diagnose this as a faulty preamp tube. I replaced the tube with a nearly-new tube (1-2 hours of previous use) and all was well. A month or two ago, the amp started doing the same thing. I replaced the tube again. Tonight, I started hearing the noise coming back. So... * Am I just unlucky? I haven't use the same brand or supplier when replacing tubes. * Are tubes just that crappy now? And I should expect to use 4-6 tubes per year? * Is something wrong with my amp? * Could a power issue be the culprit? My amp spends most of its time plugged into the same place.