I don't understand the marmots going thru packs. If packs are clean of food and all food is in a bear can (as required on this trail) there should be little problem with marmots other than begging (unless something is overly seasoned with sweat/salt).
It could be traces/smells from food that was once in the pack, and they figure it's "worth a look".
I have a couple of big plastic tubs I use in Yosemite campgrounds for camping gear (non-food) like lights, pots/pans, lanterns, etc., which would overfill the bear box. Rather than keep them in the car, even with no trace of food, I leave them out so a bear can explore them without ripping my window out, should he so desire. And at least once, they've done just that, with no harm done except picking up the items that were dumped out.
To a marmot, if pack=food, just seeing it may be enough.