Yes mine makes a noise/sound - I would call it more a 'tone' then a 'hum' ~440Hz roughly A-note 1st Str 5th Fret.
But hearing physical sound does not necessarily mean there is electrical noise / hum . . .
Are you hearing a 'tone' (as described) from the unit or from your sound system?
I figure the piezos are inherently immune to EMI problems, humbuckers should largely avoid the issue too . . . .
Has the guitar ever been rewired? Coil-taps or splits? Even just resoldering of anything??
Maybe try your setup at your friends place? Get him to check earth system on guitar - particularly string/bridge.
Can you also check with other mag pickup guitars?
Hope we can sort it out . . .
KMI StringPort_1650, SoftStep_VK2 v1.2 & MIDI Expander; Mac_Moore Guitar,
Roland VG 8, 88 & 99, YamahaVL 70m; OSX 10.6.8, iMac i7 2.8G QC; MaxMSP 5.1.8, Ableton Live 8.2.2, M4L, SC3, QC, cSound, etc, etc,