hey
my car also has the 722.4 transmission and it occasionally makes the whistling noise you referred to when selecting Reverse.
here's some info i have found on the problem:
see post #6:
http://www.peachparts.com/shopforum/tech-help/106565-help-oil-leak-urgently-requested.html#post733559
and below are two attachments that i converted from pdf to jpeg . one covers slipping reverse, the other whistling reverse.
good luck and let me know if you manage to fix it