getting humming when i connect my delay on the effects loop

[antonis]

i have a gh100l. when i connect my boss dd7 on the effects loop i am getting fairly loud and annoying humming all the time, even when the dd7 and my guitar's volume are both turned off.
i 've already tried insert and side chain, same shit
i am pretty sure i am connecting the stompbox correctly (send-input, return-output)
the stompbox works btw, but it just hums all the time
i 've tried other stompboxes (chorus and distortion on the effects loop), to see if it's the dd7's fault, and they hum too

what am i doin wrong

[scottWTBR]

hey mate are you using a regulated power supply? i got this problem using a cheap wall wart, got a decent regulated supply and it went away