Noise can also be attributed to static build-up on a particular antenna, from things like wind or snow or even rain. Just because one is building up static doesn't mean the others have to be.
A good DC to ground static suppression scheme can be had with some impulse suppressors. Not the Polyphaser unfortunately, they are just gas discharge and only work if charge build up is substantial making its own noise BTW. So the PolyPhaser stuff only is connected to ground on one leg of a dipole (depending on your balun type). Also DC shunts are not necessary if your tuner inductor shunts to ground (many don't) and it's actually grounded. However the idea of having arcing or high voltage running through my tuner isn't something I like (unless its coming from my transmitter). So I tend to use DC shunts anyway.
Products like the I.C.E. 300 series (now made by Morgan Manufacturing
) have an shunt inductor to ground that continuously bleeds off static, as well as the normal gas discharge tube.
Here in the NE, I always use some type of DC shunt to ground to bleed off static on my dipoles. Whether its on coax or ladder-line fed antenna systems. It does reduce the noise quite a bit for me on receive. On my ladder line, in addition to large horn gap suppressors, I also use large inductors on each leg to ground. They have a high enough reactance to be invisible at RF but pass static to ground. They are about 8" long and about 2" in diameter 16awg enamelled wire wound on teflon cores. I carefully match them and mount them carefully to avoid creating any imbalance on the feed-line. I never liked the shunt resistor method. No matter how high the value RF ends up going to ground.
Man-made noise is another thing and can usually be reduced slightly through prudent use of the directivity of the antenna, as mentioned in an earlier reply. However, if the orientation of your dipoles are similar, man-made noise sources may not be the issue here since this would show up on all the antennas on the same or nearby bands, most likely