If you've played other tenors and this doesn't happen you could go see a good repairman about it. It might be a key height issue or it could be that your left hand rods have play in them causing the pads in the left hand to float around. This would cause significant leaking, not so much that you can hear the air loss, but that the notes might not have the same definition. That was my experience at least. I had to have a fatter rod placed in the left hand and the keys swedged.