I run a full wired setup: PC connects to router in living rm, from router I run cat6 to switch in study, HDHomeruns connect up with switch.

I may be on to something though; I installed an app on my phone today that shows signal strength for the HDHomeruns and monitored it every now and again. At some point I noticed poor signal and walked around the house. I found the basement recessed lights on so I turned it off. Instantaneous perfect signal! So I turned it on again. After 2-3minutes the signal dropped. Turn it off. Back to perfect. I have not run conclusive tests (e.g. watching live TV) but it seems to be part or all of the problem.
When we moved in I noticed a weird buzzing sound in one of the recessed lights. I unscrewed the bulb with the idea of replacing the fixture later but have never gotten around to it. Not sure what is causing the buzzing and don't care - I'm yanking that crap out this weekend!

What type bulb is in the light fixture? Incandescent, CFL, LED or Low Voltage Halogen?

Newer recess cans usually have a thermal overload... if it gets hot it may not switch open with absolute 'toggle' from on to off. I've observed several that simply start to open and the result is arcing across the internal contact of the overload. Some older lamp sockets are simply corroded which results in arcing.

A common cause of overheating is use of a bulb with to high wattage rating. Another is insulation too close to the fixture, trapping heat.

CFL bulbs are notoriously noisy in an RF sense. Some of the new LED bulbs are as well.

There is no bulb in it - I removed it when I noticed the buzzing originally. Not sure why it is buzzing because it does not do anything special - just a regular 65w housing. Regardless - I'll just replace it as it is cheap