I wanted a single 2 button foot switch that would fit on my pedal board and could pull double duty between my Peavey & Fender amps. So I bought this FS, which works fine with my Peaveys: https://www.amplifiedparts.com/products/footswitch-marshall-two-button And this adapter to plug into the rear of my silverface Pro Reverb: https://www.amazon.com/dp/B000068O5C/?tag=tdpri-20 Now on the fender there is serious buzz when the reverb is on. The buzz gets louder with the reverb knob until 7 when it develops into a full-on squeal. I'd checked the schematics for reissue fenders that use a single TRS plug for the FS against my Pro's. The only difference I see between them is where the FS grounds come together. The newer style has the grounds connect inside the FS, then use the sleeve to connect to chassis, whereas the older rca plugs keep the grounds separate until they reach the chassis. Have I created a ground loop by splitting the FS grounds with the adapter? If so, the reverb driver's cathode is grounded directly to the reverb FS jack, inside the loop. Could this cause the squeal? Maybe I can lift the sleeve connection on one leg of the adapter.