I'm a beginning flute player. When I play, I often- but not always- have a "shh" sound along with it. I noticed that it usually starts out pretty quiet when I start practicing, but after I play for about an hour it gets totally out of control. And since I usually play for an hour or more in one setting, that is a major problem. I've tried changing my lip shape and tilting my flute back and forth, and I found there's a spot where it doesn't sound as bad as the other spots, but the shh sound almost never fully goes away. Anybody know how to help with this?