I recently had a 60hz hum after my house was re-sided. After much troubleshooting it turned out my siders were too lazy to connect the ground cable from the cable demarc on the side of the house to the grounding rod. They just neatly tucked it behind the cable panel and called it good.

So, i soldered the ground from the cable fixture on outside of house to the grounding rod with my plumbing torch and it made a huge improvement. Not all the hum was gone though...

So inside the house i have a 1-3 splitter right by my audio equipment, and if i disconnected the coax from the cable box the hum went away.. so i was pretty sure it was still coming in through the coax wire. On the splitter was a ground connection but i had nothing to ground it to.

Here is what I did, not that i recommend this to others (use at your own risk and all).

I took a 3 prong power cord, cut the female end off and shrink wrapped the hot and neutral and fixed the ground to the splitter and plugged it into the wall thus grounding the coax (again). That took care of the last of the hum.

FWIW.