This is a bit of a puzzler for me - Noise coming in on unbal

[alexdingley]

Hey all...

So I've got a lovely home studio space here in the suburbs of Philly and I'm close to public transportation.... REALLY close to public transportation. Outside my apartment window, and about 15 feet away, stand the electric overhead lines for our regional rail system (SEPTA Trains) in the Philadelphia area.

I think this noise might be new... but for several months now I've been noticing a strange high-frequency noise bleeding into my unbalanced audio lines in the studio. So, it's just effecting my guitars... everything else is balanced.

This noise comes in seemingly random bursts, for different lengths of time... they don't seem to line up on either side of when a train is coming by... and they might happen during a train passing or not. What's really interesting is that none of my -10 equipment (record player, home theater) seem to be effected by the noise. it just seems to show up on the guitars that I plug into my amp, and when I plug my acoustic into a DI box and directly into the console. I also did notice this sound showing up on the 1/8th inch unbalanced line coming out of my mac into the console...

So, my microphones aren't getting any of it on their lines, none of my balanced signal sends/returns to or from the console to my converters... no signal in my monitor lines... nothing in my effects sends or returns... just the unbalanced guitar level gear seems to get it... and my computer output.

here's a sample. it's not supremely loud, but it is ugly sounding.

SEPTA has already gotten back to me to talk about the issue, and they are going to listen to my audio clip and see if they can figure out the source... but I thought I'd throw this to you folks since there tend to be smart, experienced minds on these boards.