The thing on getting a good signal with a power line carrier is getting and keeping a perfectly good 360 degree sine wave. With today's modern toys, appliances, TV's baby monitors, cordless chargers for razors and what ever else you can think of dumping noise back onto your power lines, good signals are hard to get. On the link you checked out, Niall C. could not have answered it better. Without spending a fortune on test equipment, do some research and find a good quality surge suppressor strip that will give you good power quality. One of the best is a good UPS.
But the problem is all the noise in your house, and keeping whatever you do to correct the noise and keeping it from treating your PLC signal as noise. It's been years since I've had to do this kind of trouble shooting but it all goes back to what Niall C. pointed out. Unplug electronics, turn off breakers, try surge strips and or a small UPS system. Remember just because you have noise at one time today does not mean you will have noise the time everyday, so try at different times of day.
The cheap way is trial and error. I'm sure you are not the only one with this problem today so keep googling and checking chat rooms dealing with this kind of technology. If you want a quick fix, you'll have to pay for a professional and with noise on power lines, even it might take them a few trips.