excluding air escaping from the mouthpiece area which is distinctly an embouchure issue (not taking in enough mouthpiece in accordance with the mpc design), alot of the air escaping sounds is attributed to the setup of the instrument.
For instance, if a pad is too close to the tonehole this can create a air hissing sound.
Also, if cork pads are installed an a bit too close and the corners are not rounded on the pad, this can create an issue.
basically any pad that is too close can affect the airflow out of the tonehole and create a airy sound.
This excludes any buzzing sound which can easily be created by the pad material itself buzzing in the airflow.
But if you like to really push a ton of air through the instrument you may still have these issues.
Also too close of pads can create notes to be flat.
One particular note to test is a E just below the staff T x00-000 This note is a good test on the setup of the instrument.
For instance, the note may have air escaping sounds and may sound stuffy or even flat.
If you rotate the clarinet upper and lower joints so that the bridge key is not part of the mechanism anymore you will notice that they key now opens alot more. Then play it and note how it sounds. If it sounds alot more open and less airy then the cork material under the lower joint bridge key is too thick (or the pad is installed too low in the pad cup).
This would also be the issue if the C sounds airy T xxx-ooo as the silencing material under the lower joint bridge key is too thick (and/or the pad is installed too low from the pad cup). So if one simply uses some sandpaper (220 or 300 grit works good for this) to thin the cork material (cut a small strip and move it back and forth under the bridge key, blow it away, and retest the tone until you like it).
But many clarinets I've seen simply have too much cork thickness in many areas of setup.
On lower cost setups this is usually the problem in all areas of the clarinet.