Something's leaking. First thing I'd check is the set screw over G# (actually the little lever next to it). Make sure G# isn't opening slightly when you press the left hand table (Bb,B, and C#). If it is adjust the set screw so that G# remains firmly closed when you hit the LH table. If that's not the problem then check the octave vents, make sure they're operating properly. Also maybe eyeball the LH palm key pads. Sometimes crud can build up on the pads (especially F) and cause a leak.