someone will correct me, but I was once told a normal huco type coupling is only good for 14000rpm anyway. I personally now prefer rubber /flexi type couplings like those supplied by mobile marine. there are other suppliers!!!
normally noise is made by vibration, this can be caused by misalignment of the coupling, motor, propshaft. in some cases i have had the motor mount flexing causing this (cheap motor mounts!) the coupling not being snug enough, or the propshaft sliding in the outer tube! also there is some discussion as to the distance between the propshaft coming out of the hulll and where the coupling is, ie the amount of unsupported area of the propshaft to the coupling, more relevant to m2 /m3 props. Also the type of propshaft, is it a proper metal bush or a nylon bush?? is the propshaft bent (roll of glass to check).
But in your case it could be that if your building the matchbox/revell flower, then its the fact that its a plastic hull, very unforgiving for vibration and noise!