I have marlin model 336 30-30 with a loose trigger, it jiggles back and forth easily. Does anybody know why it does this? The rifle shoots well, but I've never seen a rifle or any weapon with a trigger like this. If anyone can help me with this I would thank them.

It's made that way. The trigger isn't fastened to the sear, but pivots on a common pin and the sear spring doesn't touch it. I don't worry about it, but you can fix it with a Wild West trigger. You can see how it's put together here:
http://www.gunuts.com/view.php?view=details&model_id=40&type=2

Bye
Jack