Welcome to the site. Birds and other animals do have a way of worming their way into our hearts and helping to heal. They are amazing and yes they are addictive. I started with one tiel 2 years ago and I now have six birds. Both my tiels are girls so they make noise and that is it, my daughters male tiel whistles. Here is a site that should help with your issue. I cant whistle at all.
Birdie's Domain - Tunes for Tiels and other fun stuff