Yeah i had the exact same issue 2 years ago, that why i sold it back then.
I thought i would give it another go and bought a new system this year.
I was getting strikes plotted at around 800 miles, so i knew that the signal must be weak, so i bought longer cable, moved it further, moved it higher (about 5 meters higher!) and ensured i had a few walls blocking LOS of the energiser.
Not sure if the type of cable made any difference, but i got shielded cable (STP) too, not standard patch cable(UTP).
I am currently running the system with 0 squelch and its running fine (though this time i am running lightning 2k) as nexstorm keeps coming up with loads of noises or strikes, lightning2000 seems to know what they are and ignores the fence.
My advice, try giving the detector some more height, try and block the LOS of the device causing the issues. Maybe give L2K a go, see if that helps, if not come back here and ask.
Looking at windy's current nexstorm page, think he may need to try those(if not done so already)

(that what mine used to be, 58-60 strikes a minute though)
http://www.weather-display.com/windy/gb/nexstorm.pngStuart