I had a similar problem with latest sierra, and support provided me with the following, which worked (they guided me to the below links, bypassing Monkey):
The driver installation has changed on High Sierra:
http://line6.com/support/page/kb/_/recording/computer-audio-set-up-and-troubleshooting/macos-high-sierra-1013-driver-installation-change-r879
Please check out the Security & Privacy seetings on your iMac and try to reinstall the latest Mac driver v7.6.7 (without using Monkey). It can be downloaded here:
http://line6.com/software/
However, I'm now getting the static as well, and while it went away when I swapped out a USB cable, it's back again regardless of cable. If you get a solution, please share.
Best,
Phil