Sorry Opman, we have sorted it! it was, as Jay and you all expected the masterlink cable. but i cant work out why.. something to do with a join in the middle. i am going to do a bit more investigation and will post what ever i can find for future reference.. a really wierd one, and getting weirder but i will find what was causing it. andway at least i can listen to it while i'm thinking about it!!
Thanks to everyone for their assistance and suggestions.. back to you once i have something conclusive.. give me 48 hrs..