The led issue is ghosting. You can either put in non ghosting bulbs or led flicker eliminator boards. My lightning will be getting the flicker eliminator boards very soon.
The hum can be caused by bad caps on the sound and speech board, old sound cables or a worn out speaker. My speaker cone disintegrated the minute I touched it. Parts express has some nice cheap 6.5 mid range subs. I can look up the one I used if you want. If they have never been touched I would definitely recap the sound board and replace the sound cables.

Every bulb in my lightning is a Comet led, the least expensive ones they sell. Some are color but most are frosted warm white. The flicker isn't that bad so I really haven't been pressed to put in the flicker eliminator boards. Eventually I will because what started out as a project pin to learn basic repair has turned into one of my favorite pins. I will never understand why this pin is rated so low.

Sounds to me like the issue is at the rectified board. Have you rebuilt it?
What about routing the speaker wires away from the harness?

The sound loops through the speech board so it is possible that the issue is the pins on the speech board. I had to reflow mine because speech wasn't working at all. I also crimped on new terminals.
As a test you could temporarily move the speaker and wires to the back of the cab but I highly doubt that will fix it. I would reflow the pins on the speech board and put on new terminals first.