This may not be especially helpful, but I can tell you one way NOT to do it.
I ran a pair of standard (non shielded) in-wall speaker wires from my receiver up through the front wall of my living room, through the attic, and down through the back wall to a pair of subs (SVS PC12 NSDs). One of the speaker wires on the back wall runs down the wall parallel to a power line that runs down to an outlet (the speaker wire and the power line both run in the same vertical passageway between a pair of studs). This sub (left) has a significant hum. The vertical run for the right sub is well away from any power lines, and it does not hum.
At first I thought it was ground loop hum, but I tried connecting the left sub to the same power outlet as the right sub, and it made no difference.
I'm planning to replace the speaker wire with RCA lines (Blue Jeans LC-1), and run the RCA line down in a different area so it is not so close to the power line.
I'm not sure if switching to RCA cable by itself would solve the problem. I suspect that running the RCA line right next to a power line for about 10 feet might be too much for the RCA to shield.
To be honest, so far I've been too lazy to replace and reroute the lines, so I just turn the power to the interfering outlet off (it's tied to a wall switch), which eliminates the hum. Somehow, every time I think about spending 4 hours frogging around with this, there is something else that sounds like more fun, and turning off the switch "wins."
