Update :-
Today I got some work done and also tried a couple of things but nothing changed, still the same issue, everything will run fine at spindle speeds of 2200rpm and below.
Even tried a different PC with a different version of Mach3 and a different Smoothstepper Plugin, I didn`t transfer the XML file from the original PC, instead I opted to do the new one from scratch, still exactly the same.
As for "noise" issues, I even got an old mains drill that the brushes are shot on and ran it inside the mani cabinet with all the electronics, it is so bad that at around 5~6ft from a radio it blanks the radio, didn`t make any difference, should have sent everything haywire in my mind.
Regards
Rob