This happens to me all the time at work. I've got half a dozen VMs open, then I realise it's going-home time and want to pack up and get out of there! Even though I pause my VMs, and it looks like they're suspended, and I can close Workstation, it's still doing stuff in the background. The disk churns like crazy. It once took fifteen freaking minutes for it to be done doing whatever it was doing.
This hint from Bryon Brewer worked a treat! Thankyou, Bryon!