"When air passes by an object at certain speeds, a strong pure tone, known as a Karman tone, can be produced. This can be prevented by making the object longer in the direction of flow, such as with a "tail," or by making the object's shape irregular." -- http://www.nonoise.org/hearing/noisecon/noisecon.htm#SOUND PRODUCTION IN AIR OR GASES
You could wrap weatherproof cord (Dacron is good, if I remember correctly) around the guy wires at about one turn per foot or so. That is supposed to affect how the wind spills over the wire and break up the flow. I have seen that recommended for stabilizing tribander elements that are vibrating in strong wind (discussed in the Antenna Book, IIRC), but you see the technique used everywhere--from the spiral around modern car antennas (no, that's not a helical antenna
) to smokestacks http://www.nonoise.org/hearing/noisecon/c1exam.gif
As an alternative, you could also use different gauges and tensions for each of the guy wires to get your antenna play a nice chord. Experiment!