An irritating noise
made by a fly
Also, for an extra-terrestrial to cruise by Earth, land near some poor sod who nobody is ever going to believe, wear goofy antennae and make "Beep beep" sounds.
Rather childish, really, though they do come in handy for intergalactic hitchhikers.
Also a small background presence, not in the front of your mind but distinctly there, slightly distracting.
I have it on a very good authority that "buzz" can also mean getting blown out of your mind on alcoholic substances, as in "You idiot, you bought Sharps beer. We cant catch a buzz on non alcoholic beer... =( "