Rob is correct that you shoudln't be spending money without sorting the problem. While the Cslabs are good with noise this doesn't mean it will cure your problem. The noise could be being picked up in number of places, the signal cables to drives for instance which are between Cslabs and Drives.

You NEED to find and remove the noise at the SOURCE. Buy mains Filter for both the Control box and the VFD before buying anything else.