sucking air

["Dan Hagrman"<danlh@qdeck.com>]

Hi again All,
reading my new Alfa book, it says that you may have emissions
trouble if you hear sucking noise when you take off the gas cap,
and that a "cheap" fix is to drill a hole in the cap to equalize the
pressure.  I believe, when refilling the tank, my Alfa tank is
"pressurized"  - i.e. the cap, if unscrewed quickly, will actually be
blown off the filler tube.  Yikes. (?)
1. Is this bad?
2. What can be causing this phenomena?
3. Should I drill a hole in the cap (I don't know if it's stock or not -
it's relatively flat, simple, and painted black)?
any ideas will help. thanks,
Dan in Mo with an '89 Veloce (such a pretty car).