Is this a new problem? Or has it existed to some degree for a long time?
Yes, a line conditioner would help. BUT, as noted by others, how much line conditioner you would need is going to be a huge question.
Personally, I would start with an inexpensive line conditioner. Rat Shack sells a nice multiple outlet HT unit for about $55. But even that one could be overkill for your needs.
Why the inexpensive units? Well, comparing units in the dreaded Monster brand, the biggest improvement between their $50 unit and their $200 unit is basically the number of outlets, telephone and cable outlets, and the joules of surge protection. There is some internal noise reduction features, but the amount of noise isolation improvement to be had with those features is minimal.
Start cheap, 40 or 50db of noise reduction could be all you need to improve the problem.
By the way, yes the problem could be with the airport. Relocated antenna, new more powerful broadcast equipment, repairs or maintenance on existing broadcast equipment, changes in air traffic patterns etc etc.... good luck in tracking down that kind of information.
Or the problem could have absolutely no correlation with the airport.