High-tension power lines and audio

This may not answer your question about the effect on performance but may tell you something about these lines and what they are all about. The lines you are refering to sound like what may be a "345" transmission line. "345" refers to the voltage carried, which is 345,000 volts. Your house is just outside of the power companies right of way, by the way. There are even higher voltage lines in some areas of the country. In the state I live in, this is the big dog of trans lines. I can assure you that they DO put off quite a bit of energy. I used to be a transmission line walker for the electric company, and my job was to assure that there were no hazards in the form of trees or brush that could possibly contact these things. Often there is a two track under portions of this size line that would allow a 4WD vehiche to follow the line. On a particular line I have worked, every time you park the truck under the lines for any period of time, you would get a huge static poke off the truck when you touched it to get back in. The truck must have acted like a storage battery for all this voltage in the air. The line is about 80 miles from the generation facility to the sub station. As you can imagine after being poked that many times I got conditioned to not want to touch the truck, even in the morning when I got in it after it sat in my driveway overnite. It took a few days for this "Pavlov's Dog" effect to wear off. Linemen that work on this voltage circuit have strick guidelines that they must adhere to as far as safe distance that must be maintained, since these things can arc a great distance and kill you without even physicaly contacting the things.

yank just wait until it rains: you'll hear & see the corona discharging around the insulators & smell the ozone in the air. This generates a LOT of EMI/RFI & you may or may not notice some noise pickup issues in that regard. If you like any AM radio broadcasts - well forget it! Any marginally designed componentry may be somewhat penetrated, but quite likely there won't be any big problems.

I hyave lived near power lines abnd I feel no evidence of dain bnramage.

Perhaps not so unsubstantiated ....
http://www.powerlinefacts.com/Leading_authorities.htm
But I think for a one year period it is probably not a problem, so long as you're not planning to start a family.
I always apply the precautionary principle. If there might be a threat, but experts disagree, then avoid until experts agree.

As for audio performance I would expect it to be component dependant, since component design will dictate its susceptibility to EMI. However I would be surprised to have interference on anything other than FM and AM radio.

I should mention that I am aware of the unsubstantiated health risks of living near this type of tower. We will risk that aspect for the one-year period. Just wondering what to expect regarding audio system performance.