Well...a defective modem is one possibility as you said...and you already answered my question as to whether you have called your ISP for the possible news that there was cable trouble outside your home or down the street. It could still be a line that runs from the pole to your house. But not likely since you did not say anything about having cable TV problems. During the "brown-out" with your modem, have you the possibility of running into where the TV is playing and seeing if its also on the fritz?
If it is outside of your own connection to that pole, then somebody else would be complaining.
Another silly question until I have explained it...Is it raining these days up there? I once had a phone line go out on me and it took the repair guys four days to realize that the wire was frayed on the inside of the wall from the outside and that rain water was causing a short.
These are just ideas that come to me as I think about your problem. I hope one of them might trigger something more useful in somebody else's post...
__________________
|