Squeal on the 3 draw
When I bend the three draw on my Lee Oskar or Suzuki Bluesmaster in D, the note sounds, but often turns into a squeal. I can bend more or less okay on my other harps (from low F all the way up to F) and don't get the squeal. However, I won't immediately assume it's the harps that are to blame since whenever I get a problem it usually turns out to be my technique that needs adjusting - and I get the same problem on two different harps in D. The problem is worse on the Lee Oskar, which seems much tougher to play. My other harps - Special 20s, Marine Bands, Blues Harps, Promaster, Crossover - are much easier to bend by comparison, even the F harp. Does a squeal mean I'm bending too far, and is there anything I can do to the harps to make them easier to play?
Lee Oskars are especially prone to this squealing behavior, but you can get it out of a lot of different harps if you try (or if you're just unlucky).
What's going on is that even if you're not trying to bend a note, your mouth resonance is set to something the reed picks up on but can't respond to, so it squeals. The squeal is believed to be caused by the reed rocking from side to side (torsional vibration) instead of (or in addition to) end to end.
There are two solutions to the problem (crossing your fingers is a third possibility).
One is to work on your mouth shape so that you don't accidentally fall into squeals.
The other is to put a dampener on the surface of the reed, about two-thirds of the way back from the tip. The dampener could be a small rectangle of adhesive tape, a dab of glue or nail polish, or even a lump of wax. The important things about these dampeners is that they don't go over the edge of the reed and interfere with its movement through the slot, and that they don't add enough weight to change the pitch of the reed.