apogee duet 2 hum / grounding issue?

[Rufio90210]

Hi I have an apogee duet 2 , using garageband on macbook. Whenever I run my guitar through xlr or instrument input I have a very loud hum that does not go away unless i put my hand on bare foot on the apogee. Its becoming annoying playing guitar with my foot on the thing any advice on how to sort this out?

Luke

 

[JLondon]

do a google search for "ground loop hum"