When I have a warning crop up in some module, I usually debug it like any other code. After looking at the code, I insert print statments to see what is going on. If that does not work or for some reason I cannot alter or override a method, the perl debugger is always helpful.

If you want set a package's verbosity level, just reach in and set that package variable. Sure, it's rude, but it gets the job done :)