Carrie,
I own the Tyros since about a week now and am happy Yamaha put the power-supply IN the keyboard.

Your 3k has an external supply, what implements the mains-voltage stays active and the supply keeps 'working', even when the PSR3000 switched off.
I expect the supply to be a 'switching' type and yes they make noise depending on the load they have to 'carry'.

Perhaps you could use 1 mains-switch for all equipment ? (with distribution block)