Hi. I have paled the flute for 3 months now. And i have a Thomson Flute. Before i got my flute, there was a practice flute at my school. Now, when i practice there without my flute, i use their practice flute. I noticed that my flute produces A Hissing sound because i compare it whenever i play their flute. When i play their flute, i have a very good tone quality and i do have a good tone quality when i play. But, in their flute, i did not encounter the Hissing Sound. I only encounter it when i play my flute. I asked my teacher if there was a leak. Then she told me it was only me, producing air. But then, i really noticed the hissing sound on my flute. Is there something wrong with it? I checked for any leaks, tightened some loose parts, and i still get the Hissing sound. What can i do about it?