Ceri,
What you have there is a TX that is slightly out of trim reletive to the IBC, not to the TX its self! its not uncommon to have to adjust the trims to get a perfect dead band. In fact with Vantec controllers I have never had one that didnt need a little trim adjustment.
As for the noise, you are right, its the switching frequency making the laminations in the motor armature sing..Vantecs do it too (but louder!) You cant do anything about it but its totaly harmless to the motors so dont worry.(I quite like it!)