Sorry for the question, got it figured out. It was the high pass filter engaged interacting with what seemed like compression and high input levels. Turned off the HP filter, dialed the compression a little harder, and backed off the input level a little. Attached is a photo of my JM47 (not sure if that was your design?) with my Fletcher-designed preamp section in the rack just to share with you that your products are still being used, cherished, and appreciated! 
