Picture & sound breaking up

[NS215]

Hi all, hope you can help, I've just had a new ariel fitted as all 4 tv's in the house were beginning to get picture & sound break up, all are good now except one tv, this one works fine on BBC1 & 2 but any other channel its breaking up or says channel not tuned, so I had a play about and have noticed if I touch or go very close to the coax where it enters the tv, then the picture returns to normal, move my hand and it starts breaking up again, any ideas what I should be checking, maybe an earth somewhere, but where ???
Many thanks for any advice given

 

[Sam Gangee]

Most of the comments on this page apply:
http://www.satcure.co.uk/tech/interf.htm

And it's "aerial".