I have been battling this for the better part of 3 years now with out really being about to figure out the cause, though part of that was because I hadn't known it was packet loss.

I have replaced my modem twice (not including the ones rented from my ISP), got a stand alone wifi router, got a network card for my PC, replaced my ethernet cables and upgraded to cat6 (even though I can't get 1gbps where I live), I've had my ISP's techs replace all the lines and the port that connects the outside line to the inside, done away with all the splitters, I've had them check the line all the way on the pole (and at one point their thing that sends out the signal was causing issues for the whole block and had to be replaced).