You get to phone up and try to remain calm. I'd consider holding the phone against the psu while it's rattling. Put it in very simple terms; the bearing in the psu fan is failing, this is evidenced by a rattling noise after several hours of operation, which ceases if the fan is physically stopped. This is very simple to test for and you are enraged that "insert name of tester" failed to spot it, and will hold ocuk liable for every component damaged when the psu fan fails and psu consequently fails.
Escalate to manager if required, you're likely to get all costs refunded to you. Given you're trying to replace the faulty psu with an identical one it's unlikely that you've decided to waste your own time and money on sending a working one back.
Good luck.