when I bought my 2017 off-road 4x4 back in May it had a light electrical hum after shutting off engine (about 20 sec). After installing an aftermarket Amp and speakers (maybe coincidence) that light hum became a slightly louder hum. I can now hear the hum inside the cab. When I press the engine start button once (without pressing on the brakes to actually start the engine) the radio and aftermarket amp and speakers turn on. There is no hum at this time. I press the start again to ignition (all the dash lights turn on) the humming starts. There is humming even if the radio/amp is on or off. When I press the start button again to shut everything off - dash turns off and the humming continues for about 20 sec and then turns off. I tried disconnecting the 4 gauge wire that runs from battery to amp but that did nothing. Maybe this humming is normal - I don't know. Seems like the sound is coming from the alternator area. It's not from the fuse box behind the battery. I opened the lid and checked. Any ideas?