You could also add these two lines at the top of the main ai script for any entity that has its Always Active = YES...
:scancodekeypressed=51:ambience=25
:scancodekeypressed=52:ambience=25
Of course you would need to set the ambience to whatever you want it to be, as we used 25 for this example.
So, in your case it would be...
:scancodekeypressed=51:ambience=3
:scancodekeypressed=52:ambience=3
This doesn't set the ambience, so do that how you normally would.
These two lines simply disable the < and > keys
It may flicker a bit when they hit it because the engine still tries to adjust it, but it should keep them from makes any drastic change.