In case anyone else has this issue: turned on my GNR LE a week ago and had no audio. Just random āpoppingā sound from sub every 5 secs. Troubleshooting found I had audio from CPU, headphone jack, and post ground loop isolator (tested all using headphones). But nothing from the machineās speakers. 12 volts on J100. Confirmed fuse continuity outside of the circuit. Assumed the board crapped out.
Replaced the sound amplifier board after triaging wl JJP. Was disappointed to find the issue persisted.
Started looking to remove variables and found the sound returned after unplugging the sub hookup from bottom left of the sound board. Apparently I have a short in my sub. Previously was running external sub via alligator clips off of the factory. With the new board I now have a blue audio out jack (to go with the green input jack; my October 2020 build had an older version of the sound card). Replaced the alligator clips with 3.5mm to RCA direct line input to my external sub.
Cabinet sounds great - even though Iāve left the OEM sub unplugged. Going to order a new internal 8ā sub so the cabinet doesnāt havenāt any asterisks on it. But: back in action.