Driving Horse Periodically Making Noise

[Crostler]

The answer is in your last sentence I believe, horses with a dry mouth will often exhibit all the symptoms you mentioned. You need to get her salivating, bits that help with that are the older bronze nickel plated bits. Stainless Steel is very popular these days but doesn't help horses to salivate. Also there are bits that have little "ticklers" fitted to the inner section of the bit, the theory being these encourage salivation and for some horses they are successful.

Obviously you may need to try a few strategies to overcome the dry mouth, but I'd like to be as sure of winning the lottery as I am that is her main problem.

As Danno stated, there are plenty of issues that may cause this. Did you make your own research?

[KTQ]

So they ruled out a soft palette?

Did you try tying her tongue AND putting on a drop noseband? Try also giving her Airway gel and using a nebuliser on her. Try also giving her a Rakelin injection once per week to calm her down. Our filly roars and the vet said we'll need to retrain her to swallow when she's racing. She tends to stop swallowing when she gets stressed by work and then roars, cuts her wind off and gets more stressed - it becomes a vicious cycle. If the above doesn't work, you may need to get her operated on.

You can also try Glycerin or Wind Aid over the tongue before she works
Edit: I see you tried Wind Aid