I just wanted to pass this on: I was experiencing a problem with line hum from the plate amp of my Tempest. I had purchased and installed the AMP350 plate amp late last year and begun to experience this problem after about 3 months of use. The hum began at a low level and only got louder and more noticeable over time. I tried the usual approach of repositioning of my home theater's power cabling, checking all my interconnects and I even attempted using an adapter on the power cord (which is dangerous by the way) but it still couldn't resolve the hum problem. I had read in the forum that some others had suggested that some amps have power supply transformers that would create this condition if they weren't mounted securely to the backplane so I decided to remove the plate amp from the rear of the Tempest and inspect the mounting. It was securely fastened so I powered it back up. I determined that the transformer was not the source of the humming so it had to be coming from some other component. I decided to rotate the crossover, level and phase potentiometers and discovered to my surprise that the source of the problem was coming from the phase pot when I rotated it!! I had some Radio Shack Tuner/Control Cleaner & Lubricant handy so I powered it down, removed the control knobs and unscrewed the circuit board from the backplane. I then sprayed some onto the pot's contact wiper surfaces through an opening in the casing and exercised the pot. Viola!! It solved the problem! I'm happy to report that the amp has been working well since . From this experience, I've learned that potentiometers can also be a source of hum and/or noise as well as power supply transformers. While this little tip may not be applicable to everyone's situation, I hope that this may help someone else with their amplifier humming problem. Cheers!