Under the Levels tab you will find something called "PC Beep". It can be turned off. This PC Beep is the culprit.
I only had it [the beep] showing up when I clicked on a song from the Search window as well. This is a Vista thing, not Hoster.
Once I turned off this PC Beep I am able to add tracks from the search window with no more beep.
Attached is a Disable Beep document. I have not tested it. Maybe Admin can. It might work on more machines than the fix I found on mine.
ADMIN NOTE: This didn't work for XXYzz as seen below. Is there on true work-around for the Vista bug? Can MTU find something related to using dialog boxes (the Search method) that can "disable" beeps? 