Thanks Guys!
Lots of things to try
Only thing I've done so far is switch the USB connections. I had the Virus and Maschine plugged into two USB 3 sockets next to each other. I've moved the Virus to the other side of the laptop and into a USB 2 socked (and moved the mouse onto the USB 3).
Only tried one synth so far - Rounds - which was causing noticeable crackles an it's a def improvement but still need to do more testing.
Fingers Xed!