Update,
It appears to be power supply,
When machine first turns on power supply starts as normal (fan goes whrrrrrrrrrrrrrrr)
After some use (possibly when power supply gets warm)
The fan starts going whrrrrr-whrrrrr-whrrrr
With momentary pauses, which coincide with the laser loosing g power momentarily.
But once it starts, the power supply continues doing this after the job is done,
If I flick the laser power button,
The fan goes back to normal momentarily before power goes off. And if I leave it 5 min and turn it in, it stays constant....
So.... I am thinking something is over heating prematurely or a capacitor is flaking out.....
Anyone got any ideas?