As a side note, my amp (HeadRush Gigboard & FRFR108s) uses a noise suppressor at the input of the signal chain. Once the guitar is plugged in, and rigs created, there's usually this explosive noise caused by the input signal's noise-to-volume ratio being much too high.
The solution is lowering the cutoff level at which noise occurs. Depending on any of my rigs, that number can be between -85 dB and -93 dB. Above these numbers, the guitar will sound clearly through the amp. Below these numbers (heading towards larger negative numbers), the noise is cut off from making it through the signal chain.
If your church has either the funds or incentive to improve its sound through the PA, you might ask if (with your financial help) you could place a noise suppressor in front of the mixer, in case the noise occurs prior to the mixer. Remember that this is the only place you can put a noise suppressor. Between mixer and power amp won't do any good because the signal is different than from when it first entered the mixer.
For suggestions; TC Electronics makes the best noise suppressor on the market today, the "Sentry." The pedal has a learning curve and you'll need to read the owner's manual to dial it in correctly. Once you do, though, you'll realize that the noise that was driving you nuts could have been nothing more than some EMI/RFI from overhead lights or a fan.
The hum is typically 60 KHz cycle hum found in all AC circuits, some with cleaner power than others. Some circuits when used extensively (read: many items drawing power from one or more outlets on the same circuit breaker) draw too much current which contributes to the hum. If your church has old-fashioned lighting and ceiling fans, this can contribute to the problem. The. immediate solution is not replace the lighting or fans, but consider the least invasive approach: the noise suppressor. A used Sentry on eBay or Reverb might cost $80 to $110. Just do your homework and if necessary wait for a good deal before you make a purchase.