Hi Michael,
Sounds like a mystifying one. I don't have any really promising theories to offer, but here are a few things that come to mind to try:
1)Try moving the sub and monitors a goodly distance apart, if they are not presently set up that way.
2)Try putting shorting plugs on the rca inputs of the sub, especially if the previous owner was not driving them with a high impedance source such as the PVC.
3)With power off, insert and then remove a phone plug into the unused 1/4" TRS input jacks on the sub. Do that a couple of times, to make sure that their contacts are not somehow stuck in an incorrect position (which conceivably could affect things even though you are not using those inputs).
4)With power on and the whistling present, lightly jiggle the 1/4" plugs at both the sub outputs and the monitor inputs, to see if there is any effect on the whistle, due to one of them making marginal contact.
5)If you haven't already, see if the whistle occurs with only one monitor connected, and try using each of the two TRS interconnects on the one monitor.
6)Carefully compare the volume levels of the two monitors while playing a source which is either mono or centered, as a way of verifying that there isn't an open connection on one channel, on one side (+ or -) of the balanced signal pair within each TRS cable. That would cause a 6db volume disparity, and conceivably could account for the whistle as well.
If you gather from some of these suggestions that I don't have too much faith in the connection integrity of 1/4" connectors, you are right! BTW, one minor correction just fyi -- they are referred to as phone jacks, not phono jacks.
Hope that helps,
-- Al
Sounds like a mystifying one. I don't have any really promising theories to offer, but here are a few things that come to mind to try:
1)Try moving the sub and monitors a goodly distance apart, if they are not presently set up that way.
2)Try putting shorting plugs on the rca inputs of the sub, especially if the previous owner was not driving them with a high impedance source such as the PVC.
3)With power off, insert and then remove a phone plug into the unused 1/4" TRS input jacks on the sub. Do that a couple of times, to make sure that their contacts are not somehow stuck in an incorrect position (which conceivably could affect things even though you are not using those inputs).
4)With power on and the whistling present, lightly jiggle the 1/4" plugs at both the sub outputs and the monitor inputs, to see if there is any effect on the whistle, due to one of them making marginal contact.
5)If you haven't already, see if the whistle occurs with only one monitor connected, and try using each of the two TRS interconnects on the one monitor.
6)Carefully compare the volume levels of the two monitors while playing a source which is either mono or centered, as a way of verifying that there isn't an open connection on one channel, on one side (+ or -) of the balanced signal pair within each TRS cable. That would cause a 6db volume disparity, and conceivably could account for the whistle as well.
If you gather from some of these suggestions that I don't have too much faith in the connection integrity of 1/4" connectors, you are right! BTW, one minor correction just fyi -- they are referred to as phone jacks, not phono jacks.
Hope that helps,
-- Al