"The noise got WORSE after I unscrewed and then reattached the input board (during which I never disconnected where it is attached to the actual amp boards at all)."
I feel for you man, but you have to understand the nature of vintage audio gear. It seems you were pleased with the amp when you got it (based on your initial impressions and playing of the amp). I/we have no way of knowing what or how you hooked up sources/speakers to it after that or in general messed around with it (switch settings, accidental/incidental speaker wire shortings, removal of boards, etc., etc.). From your descriptions, it sounds like you have a loose connection somewhere in the input signal path. The amp was dead quiet the last time I used it prior to packing it into the shipping box. It seemed to have been working fine when you 1st used it (i.e., it did not arrive "D.O.A." nor with any obvious shipping damage). Beyond that, I have no clue what the cause/source of this static is. Clean all your signal path connections, etc. Test them on another amp. Test the speakers on another amp. Have a REAL tech look at it.... - Ed
FR: 400 disk changer with PS Audio Digital Link III DAC; Technics SL-1100A TT. QED Quenx1 IC's from DAC & TT to Adcom GTP-602 preamp/Tuner. AudioQuest King Cobra IC's from preamp to M1.0t mk-II opt2. QED Silver Spirals 4M wires to EPI 1000’s.
LR: AudioEngine wireless link from family room preamp to Barcus-Berry 2002R Sonic Maximizer to GlowPower Zyxt IC's to Sunfire 300x2 to Nordost 6M bi-source wires to AOS 28" MDF spherical speakers using six 6.5" woofers and eight 1" dome tweeters symm. arranged around the surface.
SS system: CX-995V DVD to AV-634x 3-4 channel amp (center/rears) & M1.0t mk-II opt2(fronts).
Garage: 300 disk changer to Entech 202.5 DAC to MXR150 Receiver (pre) to TFM-42 to EPI 400 speakers.