Knock/Heat Light flickering on?
 

I have just started getting my heat light flicker on and off. Happens between 2000rpm up to about 3400rpm. Can be stationary and even on the down change. I.e the engine doesn't have to be loaded or under boost.
Geff has told me it's not knock as he connected an external reader to it today. He said most likely it is interference from the trailing plug or lead next to it. Plugs are new.. what on the lead would cause interference? I didn't get a chance to ask Geff in the rush today! Can somone tell me what I am looking for or if there is a way to shield the knock sensor to avoid the problem of interefence? Could a blowing exhaust or noisy pump cause the problem? Possibly a silly quesion but as I understand the senor picks up noise?

Any ideas gratefully recieved!

Thank you
Lee