Are we talking analogue or terrestrial digital (Freeview) here?
If you still get striping on a different TV using a completely different aeriel, I'd suggest perhaps that it's environmental. Do you live under a pylon or have mains electricity delivered from a diesel generator in the basement maybe? (-:
Switch off cordless phones / microwaves / anything else electical in the vicinity, see if it clears up?
I live on the edge of a broadcast area (if you look at my block, four doors up from me all the roof aeriels change direction). Never got channel 5, ever, and analogue reception was prone to electrical interference (random static lines on the TV). Tried various fixes; a signal booster (which made no difference whatsoever), freeview box (which worked to an extent, but was a cheap box and inherently rubbish) and the end fixed it permanently by moving to Sky.
What's your neighbours' reception like, out of interest?