[zzeliminator]

Hello. I used a Mackie 808S powered mixer with my Mackie SRM-450's. No, I don't connect the 450's to the powered speakers outputs. I connect to the "Mixer outputs" on the front of the 808S like Mackie said to do on the phone.

In my regular gig, I use the 808S and 450s with only getting a minor amp "amplifier noise" noise. I was told in this normal in powered speakers.

I played in another building this weekend. The wall outlets were so weared out that just the weight of the cord was pulling out the end of the cord. And there were three light dimmers for the stage lighting. Speaker hum, Oh yeah!

I ran a extension cord to some other outlets to try to get onto another circuit, but all the wall outlets were on the same circuit.

I don't think the 450s like to run without the ground prong.

I would do this: Plug up the electrical cord to one 450 and turn it on (no audio cable connected). Do you have hum, if so, note how much. Try to clean up the hum there.
If not hum, continue to connect up your system, one cable at a time, turning on the power each time you add. You should find out where the problems is.