NonLinerarLoad,
Go to
www.churchsoundcheck.com. You have to subscribe to the forum. The moderators are professionals and they know what thay are doing.
There are a couple of things you may want to try.
Make sure all your audio is on the same phase in the panel.
Check to see if you have a "Pin One " problem. Open up any XLR connector in the path of the problem and make sure the pin #1 is NOT connected to the shell of the connector.
Make sure the gain structure is set properly. You may want to "lift" the shield off of pin #1 on the input of the sub amp to see if this clears the problem. I'm sure your engineers check all these.
You may have a problem with the crossover. I've seen this happen before. A few components wear out and cause noise in the system.
There are MANY forums for pro audio out there. I highly suggest joining Church Soundcheck. More knowledge there than my brain can handle.(Which is not much)
Let us know what you find.
Blessings
Mark