If you have a 'PowerMac G5 (Late 2005)' why is Apple not replacing the hard disk drive, hdd, - for free?
CompUSA, Best Buy, etc. sell all brands (and most models of those brands). They are no different than any other brick and mortar or on-line seller.
All manufacturers have had issues at one time or another with a hdd model or models.
In the days of the real MacOS - System 1.0 - 9.2.2, the Quantum hdds were quite stable and long lasting.
Others and I have had Maxtor hdds that sounded like a circular saw. Yes, there was a time when the spindle manufacturer, for the Maxtor hdds, did not manufacture to specifications, and Maxtor had many returns.
Western Digital hdds work fine for many and myself.
Hitachi hdds (formerly the IBM drive line) have a (60 - 90 second interval) self calibration which has been known to create an audible cat or baby like whine. I returned to CompUSA with said hdd, stating I will install any Deskstar hdd replacement, they provided, into my external FireWire enclosure. If the whine appeared - they can open another hdd box. And if that one failed - another replacement, etc. They opt'ed to refund my money. The Western Digital replacement is still working just fine.
As you will see, many persons have preferences and experiences different than others.
When purchasing the hard disk drive, whether from a store or on-line, understand the return policy explicitly.