I got my USED Trident S40 mic preamp and have been playing around. I really like it, but have a question about some buzz. Here's the scenario: Gating the signal at -63dB from within my DAW gets rid of the buzz. With NO input cables plugged in, if I turn the gain up it's relatively quiet (small amount of speaker static type noise). With the input gain over +45dB and the output gain at +5dB or more, the preamp begins to produce electrical noise, but I'm thinking that's fairly high gain. Plug the XLR cable in (no mic attached) and I get buzz (probably RF noise) at lower gain. Insert 48V phantom power and it gets a little worse. Attach a microphone to the XLR cable and the buzz significantly reduces, but is still noticeable with high gain settings. Using the instrument input (built-in DI) on the front panel produces the same as above. Hovering my hand centered and over the top of the amp increases the buzz significantly, but touching the amp chasis almost eliminates it completely. Adjusting the knobs increases the buzz and creates a frequency-sweep type hum when adjusting. I'm assuming this is due to the fact that the knobs are metal and transferring the voltage from my body (just a guess)?? If I use my DI box and connect to the XLR input I can literally crank both input and output gain and the preamp is dead quiet. The buttons for EQ in, comp in, etc. all make very insignificant crackle when engaging/ disengaging, but I'm thinking this is fairly normal. Do I have a grounding problem, does the preamp just need a good cleaning or is there some other problem? I shut off all my other equipment except my A/D converter and Mac, but it made no difference. Should I record the sound it's making?