421 buzzing noise

Just installed my new 421 and is seems much better than the Silva's that it replaces, apart from one niggle.
I am getting a faint buzzer noise once a second when my GPS is connected, position shows up but the noise is there all the time when it is shown, plus the time offset doesn't seem to work.
Can't find anything in the manual, any ideas what is wrong?

Icom tell me it is interference getting picked up from the GPS and some ferrites or moving the power supply wires away from the GPS supply.
Hopefully this will do it. :D