I think you can check it with an ohm meter, but I have no idea what the value should be.

Since this is an aftermarket stereo, did you try and put a larger ground on it? My Expedition had a HORRIBLE ground connection in the factory harness. So, I just made my own ground to the body, and it cleared up a lot of issues I was having.

 

I was wondering if I could add a ground to the radio.

Still seems strange that this was working fine then not,,,,lol.

 

I'd definitely try it. Go with something like 12 gauge just to make sure it's good.

 

The RFI caps under the hood will not cause the reported issue. If they were bad , then you'd have 1) a blown F30 & no start (if shorted) or 2) ignition noise that varies with engine RPMs, most noticeable if using the AM radio (if open).

The problems in the initial post are usually due to either a poor ground or a noisy charger. I have an aftermarket charger bought off Amazon that will cause intermittent TPMS errors on my Mariner. That same charger, if I use it in conjunction with a BT adapter and aux cord, cause the same type of interference as described by the OP. With the proliferation of cheap crap coming out of China, using a different charger isn't a test I'd relay on, even if you're using a charger provided by the phone's OEM.

Since you're also getting window motor noise through the audio, that points back to a poor ground for the audio unit. The ground loop isolator *might* fix the issue, but you'd be ahead by upgrading that ground connection.

The odometer symptom is interesting, never heard of that sort of behavior

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The odometer looking like a sci-fi display is indicative of the bad solder joint syndrome which plagues these trucks. It starts by going nuts once in awhile, and ends with it eventually going/staying blank. It's a simple fix if one can remove the instrument cluster and wield a soldering iron..

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Your audio humm/ buzzing won't be fixd by digging at plugs or sensors in the motor or at the fuse box. You've got a ground loop happening in the charger/ phone/ radio. Use ferrit chokes on your charger and aux cords (and if you're really bored on the yellow and black wires of the radio harness) and an aux ground loop isolator to fix the problem.