I'm an older player attempting to get back in shape after a couple of years off. I'm having a problem and am looking for some advice. As I build up air pressure and get into my upper register, I'm getting a sort of leak in the upper back of my throat / mouth. It makes a vibration and noise. I doesn't really hurt, but feels like its triggering a gag reflex. Once it starts, I can't play higher. More air pressure just produces a greater leak. I seem to remember this happening when I was a kid just starting, but at some point it just stopped. Any suggestions?