My best guess is that the hum is coming from the power supply. I would go after the filter caps therein.
Thanks for the advice/suggestion! I'll look into it!
Radioroslyn - you were right! Swapped out 3 power supply capacitors and it's working beautifully now!
Now that I can enjoy some tunes, I'm looking into fix other pieces of the cabinet. Are there any suggestion where I can source similar hinges for the back? The one on the left back side is broken (image attached).
Thank you again for all of the help!