No worries. XenonMan is spot on; this is usually a difference in ground potential, and if you want to avoid an isolator, then you would want to:
Originally Posted By XenonMan
Try attaching a wire from the chassis of the Directv receiver to your 975 chassis.

If you have some thick speaker wire laying around, you can back off a chassis screw from each unit, wrap the speaker wire around it, and then tighten the chassis screws back down.