Hey all. I just got my awesome mesa 400 (not the plus) and mesa 1x15 hooked up today to test it out, and after some tweaking to resolve most issues, i have a couple left that I'll throw to you guys to see if there are any solutions. This is my first and only experience with any tube amplifier, so if something is characteristic of the amplifier that I am misinterpreting as a problem, just let me know. Firstly, there is a low pulsing noise comming from the speaker, about once per second. Its not loud, just annoying. My thought is that is is something to do with the fan because changing the fan from low to high speed makes the noise go away. This would be acceptable, but then there's the added noise of the fan to deal with. Second, there is some sort of hum comming through that sounds a lot like a grounding problem, but with a slightly lower pitch, along with quite a bit of hiss. And finally,on the grounding issues subject, plugging in my jazz bass causes some sort of grounding hum. I know its ground-related because when I touch something metal on the bass or cable, the sound goes away. While this may seem to be an issue with the bass, it is not because the hum is not present when plugged into my little solid-state peavey. The humis also present, but not as loud, when I plug my P-bass in. This problem is the same for both channels. So, thanks for reading, thanks for replying, thanks for taking the time to help me out. If there are any more points of information anyone needs to point me toward a culprit, feel free to ask.