Sony KD-28DX50 'Smart' screen view problems

I have just purchased a Sony KD-28DX50 tv and whilst playing with the viewing modes have found that when in the 'Smart' mode an extremely high pitched noise similar to extreme tinnitus emanates from the tv.

It does this on both analogue and digital and is not volume related.

Any ideas on what it is before I send it back to the supplier (Digital Direct) as they are going to sting me for £15 delivery each way.

Any clues?