Hi Sue:
Just guessing, but it sounds like your breads may be overproofed. At
a certain point the acids developed by the yeastie beasties begin to
weaken the gluten, allowing it to tear more easily. The fact it is
happening more often with your rye breads is a good clue--rye is a
favorite food of yeast and any bread with rye flour in it will
develop faster than a bread without.
Are you taking the temperature of your dough after kneading/mixing?
It should ideally be between 77-79 degrees F. If it is hotter, try
using chilled water in your mix. If the temp is right on, use less
yeast (or sourdough), or less time in the fermentation stage before shaping.
Luck!
Bill