There are two different kinds of flutter-tongue. The first and most common is making the motion like you are rolling your R's. If you can do this without the saxophone in your mouth your are able to flutter-tongue! The second is a thoat produced flutter-tongue (not the same as growling). Make the motion like you are gargaling (sp.?) water. The flutter is much lighter than a traditional flutter-tongue, but is effective, and with lots of practice you can make is pretty intense. I cannot roll my R's so I use the second one. There is a way to produce the first kind of flutter-tongue even if you can't roll your R's (Griff Campbell showed me this this) Take your tongue and put it on the roof of your mouth. Try to keep to there and blow. You can produce the "rolled R" this way, or something similar to. I've had some success with this, but can't make it as consistant as I want. I need to put more time in on it. Good luck!