You're not alone
Sarahm, I'm a member of the whistling club too

.
I noticed it the day my braces went on, and six months down the track, I still whistle when I said 'f's and 'v's

. If it's any consolation, I notice it less now, but I'm not too sure if that's cos I've gotten used to it or it's cos it's dissapted any.
To make things more embarassing, my job involves talking on the radio for 12 hrs a day, with every transmission beginning with "VK..". When you hear the whistle coming over the radio it sounds even worse

.
No one else has mentioned it to me though. Whenever I've brought it up others have agreed that they can hear it, but no one else has ever brought the subject up. I don't even really notice it myself anymore.
Just another one of the joys of orthodontia!
