The new box fan I bought rattles, but only when it's set to a lower speed. If I have it on full blast it's not nearly as bad, but that level of breeze is a bit much.

The fan came with a little card that says if I have any problems I should contact them, the manufacturer, rather than returning it. Is this even worth the effort or should I resign myself to having it on full blast or not at all, or just dealing with the rattling?

This kind of rattling can be caused by things not being perfectly balanced, in which case there isn't much you can do. Opening things up and tightening them may or may not work.

>>33320549 (OP)
The rattling is probably between the fan and the window. Anchor it more tightly

>>33320549 (OP)
Regardless of what it says on the little card, your contract is with the store, not the manufacturer. If you don't like the product, return it to the store for a refund.

>>33320646
I tried some of the obvious things like making sure it's on stable ground and steadying it/feeling if there's any obvious shaking that can be stopped by me holding things in place. No dice.