Bought a refurbished Precision 5540 from the DellRefurbished site, and there's a sporadic rattle / grinding from one of the fans.

I've already taken the bottom off and cleaned both fans (they were pretty dusty, but not appallingly so), but that didn't do anything. What concerns me is I can't make the problem happen - sometimes the fan just sounds like a stuck engine, and other times it's whirring away (even under light load) but at least doing so quietly.

I've tried all of the troubleshooting steps listed in their knowledge base, also with no luck finding a specific cause.

If I send this back, is it likely to just get bounced right back to me as "we can't find anything wrong with it?". Will they even treat a loud fan as an issue if the computer is otherwise functional? Just hoping to get some feedback from people who have been in the same boat before I waste my time shipping this thing out and being without my computer for potentially weeks at a time.