Dicky hi ya there
The motors run nice n sweet and quiet. The problems, which I have sorted now were the:
Cheap - Ebay prop shafts
which I have managed to re-bush in situ with smaller bushes which fit the propeller tube properly rather than being a rattling good fit.
Couplings - I removed the red insert and replaced it with a bit of silicon tubing and the motor can hardly be heard, whilst its running at full belt. But, as soon as the red couplings are put back - its like a bag of hammers - so that is the next job to sort out.
I have tested the model in the bath - and it empties the bath quite nicely!
Drawing all of 12 amps per motor.
So, I think I am going to have Mr ACTion's heavy duty P94.