My 05 Equinox LT 3.4 Liter speakers started about a month or two wirth a buzz/hum sound out of all the speakers. The pitch changes with the engine accelerating. The only time the speakers don't buzz is when the truck is not running. Strange thing is if the key is turned to ACC position there is no buzzing/humming. I don't want to "deal with it" or spend alot of money replacing the whole system. Can anyone help me, or even started in the right direction

 

When this started was there any electrical work done to the car? Sounds like electrical interference. Bad spark plug wires or something with the alternator are possibilities.

 

It's not really strange because in the previous sentence you said the speakers don't buzz when the engine isn't running. The engine is never running when the key is in the ACC position.

I recommend getting your charging system/alternator checked and inspecting all the major ground connections. Is the factory radio still installed? Does your Equinox have the premium system with the external amp (located under rear seat) & subwoofer (located in back right of cargo area)?

 

no electrical work has been done

 

Yes I have the premium system with a six disc cd changer ,the external amp (located under rear seat) & subwoofer (located in back right of cargo area). And yes the stereo is factory stock

 

I unhooked the negative cable to the battery for 15 min to do a reboot of the electrical system, there were other posts like this that suggested it, so I tried it. didn't work

 

I was recommending that you get your alternator tested. Many auto parts stores provide this service for free. Your alternator may be starting to go bad. Noise in the radio is a common symptom of an alternator with bad diodes.

If the alternator checks good, then I'd suspect a bad amplifier. You could check this by temporarily bypassing the amplifier and listening to see if the sound is still there. If the noise is gone, the amp is bad.

First, have the alternator tested and go from there.