With careful observation of your roof next year, you may be able to observe a small amount of red light.
As you guessed, this is in fact from a particular Rangifer tarandus whose nose tends to be severely red-shifted as he departs a given residence at speeds close to c. This is that north-pole air freight you may have head about, and it is no exaggeration when they say that it is unmatched.
Unfortunately, given the very low population density (as well as total population count) in the northern polar regions, they have not experienced the same RF spectrum crunch that other regions have. If you've ever met a North Polarian, two things probably stood out: that deep, jolly laughter is of course unmistakable. But as rich and deep those chuckles are, their lack of respect for the FCC, ComCom, and similar regulatory bodies is even deeper.
Given how precise the shipping schedule is for you to pick up the interference at precisely the same time each year, it seems very likely that it is radiated EMI from a North Polarian air freight vehicle. They typically leave their spark gaps transmitting the entire time, so they tend to broadcast whatever their open air mic picks up as directly modulated EMI. It then merrily couples into any nearby antennas, particularly longer audio cabling.
You can try to file a complaint with your local telecommunications regulatory body, but the last time someone tried to fine a North Polarian, they simply laughed, "Ho Ho No!" and sped off fast enough to leave a slight glow of Cherenkov radiation.
Personally, I just try to be asleep well before any scheduled deliveries and make sure my devices are off, no mice are stirring, and no fires still burning. This usually mitigates most of the received EMI.
You can verify (or rule out) this theory one way or another depending on if you observe that red shifted light from your roof at the exact same time later this year in December.