I Have an old 1978 MXR Flanger... it has an anoying noise/hum even when bypassed. lately i built a True Bypass loop to isolate it but there is still that noise even when its switch on/off bypassed etc...... could it be the ground? the only thing thats connected to all the jacks are ground wires..
Fender Strat 60th Anniv HotRoded

Marshall 1980 JMP 2203
Marshall JCM900 1960A Cab
Valve Jr.

VOX v847a Modded
EHX Small Clone Modded
Maxon OD-820
MXR 1978 Flanger
Digitech Whammy
TC Polytune
Custom LPB-1 Boost