Thank you all for your replies. It does seem as though the problem is "home" based.
Bill-- The filter sounds a good idea and I am going to discuss it with an Electrician. It may be the solution.
Cees-- It is reassuring to know others have had a similar problem. i also have a very noisy fridge which makes quite a noise clicking on and off, not to mention computers and air conditioners.
Bruno and Trevor, I have checked all wires and Trevor - Theres no chance of anyone taking me for a ride-The keyboard is still under guarantee but the Techs I take it to are very helpful guys anyway and have checked it all over for me. It is their suggestion that it could be in the circuits at home.
Dear old Douglas. I know you love your 700, but you are a big strong man and I am only a fairly small lady and I can't lift the darn thing. The 6500 is really too heavy for me to cart around and that is the reason I have bought a PSR2000 that I can tuck under my arm. I am travelling around Australia next July and it will be the one I am taking with me. Nevertheless the 6500 is the keyboard I do all my arrangements on. It is just too heavy for a lady!!! Thank you all for your help- I know I can always rely on you guys. Cheers.Jean.