National Instruments GPIB-MAC User Manual page 4

* Be sure the computing device is plugged into a grounded outlet
and that the grounding has not been defeated with a cheater plug.
* Replace the GPIB cable with Hewlett-Packard Model 10833
cable.
If none of these measures resolves your interference problems,
contact the manufacturer or write to the U.S. Government Printing
Office, Washington, D.C. 20402, for the booklet, "How to Identify
and Resolve Radio-TV Interference Problems, "Stock Number 004-
000-000345-4.