Sounds like the classic problem with fans in general -- they tend to be inexpensive parts and often require maintenance (specifically having the bearings oiled), except that most of them -- even most case fans I've used -- often do not provide an access hole for oiling. I've had lots of GPU fans "grind" like you describe, so you're not alone in the least.
I can assure you a failing fan is covered under product warranty. You may be asked to clean the fan to see if that helps, but you've already done that (and correctly!) so that's hat.
I have no experience with Sapphire as a company.
Generally speaking with the video card vendors I've interfaced with -- those would be Matrox, Leadtek, EVGA, Asus, Gigabyte, and MSI -- most of them just do entire card RMAs because it's less hassle for everyone involved to just be given a replacement card. There's actually a lot of justification in this, and I can expand on those items if need be. My guess is that they'll probably just have you send them the card. Find out if they do advanced RMAs (where they send you a replacement card first).
I don't tend to recommend third-party/after-market GPU coolers because some card manufacturers (but not all) consider removal of the original HSF worthy of voiding your warranty; I believe their justification, both silly and understandable simultaneously, is that someone replacing the HSF on their card could damage the card in the process, then would file an RMA -- when had they stuck with the standard HSF (and/or done an RMA to begin with) they wouldn't have messed up their card.--
Making life hard for others since 1977.
I speak for myself and not my employer/affiliates of my employer.