Further to Johns' informative reply, If it's a new harp, perhaps the reed is a bit low down on the plate. If you get a jewellers screwdriver & gently push it up that will solve the problem. By the way, NEVER eat during a session with your harp, nobody wants to suck up half an old rusk while trying to be cool at the local pub jam
You can of course drink as much beer as you like, in fact it's compulsory!
All the best, Gary.