You said only one of the tweeters made the sound. Is it constant or did it happen once? Also, since its only one, why buy a pair? Vienna will sell you only one.
But first, diagnose the problem. As Zd suggests, reverse the cables from your amp to see if there is a problem elsewhere. If it truly is one tweeter, your dealer should be able to guide you. If there was no dealer involved with the purchase, email these guys and they will take care of you, assuming your in N. America:
http://www.vanaltd.com/
If not, go to Viennas website and look for the distributor taking care of your country.