Poor power in the house

I should add and clarify... with separate circuits, the common mode ground will connect across interconnects in the signal path (which may or may not be good depending on the equipment) IF the interconnects are unbalanced.

True balanced ICs between gear made for (alot of manufacturers fake balanced internally) is best.

With separate circuits, but common ground, you SHOULD be good.

Isolation transformers on the ICs is another way (Jensens are great).

For UK, 50Hz hum would be a ground hum and either lowering resistance in the ground to balance it out, breaking the ground with iso transformers would do the trick... lifting the ground at the interconnect (receive end only) works, too, as long as you don’t have lots of RF interference.

Low frequency noise could also be DC in your power (which is really bad). Talk to your power company and have them fix it. Big, heavy and whining (they tend to make a high pitched sound) transformers are all you can do to scrub DC yourself. PS audio makes great but pricey regenerators and iso trannys for this.

High frequency noise is RF and you need shielded ICs or balanced if your equipment has it.

Power issues are a pain.

furiouslyadrift

one way to fix a shunted system is to isolate each ground wire (basically a dedicated ground per device) buts usually much cheaper and easier to go another route ...

It's not clear what you mean here. For safety reasons, and to be NEC compliant, all grounds must be bonded together at the service panel.

@cleeds 

To do completely separate circuits requires separate service drops, too.

As long as the grounding points are physically far enough apart (I think it's more 30ft), I think you're good. Been a looong time since I read NEC and no idea if this to code...

I wouldn't normally recommend messing with ground path at the service side, but I've found so much gear grounds in the signal path instead of via chassis that sometimes it takes extremes to cure ground loops. Better to deal with grounding at the interconnects but back feeding can be a big problem. I recommend series protection (something like ZeroSurge, Brickwall) to avoid the problem. 

Hey at least it's better than just lifting the ground (I've seen this way too many times).