The first thing I would do is use a heavy duty power cord / power strip to plug the equipment into a number of different outlets to see if the problem still persists. If it does, then I would look to plug this stuff into a completely different circuit to see if the problem still persists.
I would also remove the receptacle itself and verify the grounding and its overall physical condition.
Big's suggestion to lift the ground component by component using a simple 50 cent ground lifter may help you to identify the affected equipment but would not be a permanent solution. Lifting the ground is dangerous and is a definite electrocution hazard.
I assume you will be using a power protection device for your system. Most of these filter the power by internally balancing the power back and forth several times to eliminate most external noise. If you have checked everything else out with your house electrical system and find no problems, then I would plug everything into a power protection / isolation device to see if this solves your issue. But if you have OCD tendencies like me, I would still try to isolate the route cause of the noise coming into your system. I would be very interested to know what you find out.