If it's making more noise then it should it could either be bearings or more likely probably the heads crashed.
You won't be able to "open it up" and replace the drive with a SCSI drive. The 128k/512k did not have SCSI ports. The hard-drives at the time connected to the external floppy port. They are nothing like the external SCSI enclosures used on the Macintosh Plus and newer machines. The only other hard-drives you'll be able to use with it is other drives that also used the floppy port. I could be wrong since I never worked with these older machines, but I'm pretty sure the hard-drives at this time were not interchangeable. You wouldn't be able to use the enclosure for anything other then the exact drive that was in it. The controller board may have also been part of the main logic board of the drive it self, so that would also make it impossible to replace the drive in the enclosure with anything other then that exact drive. Unless you can cram a different brand/model hard-drive in there that also used the floppy port.
But such drives always came in an external enclosure (unlike the SCSI drives which also had internal versions) so that wouldn't make much sense and you won't really find them sold outside of the enclosures they came in. With the 128k/512k, your best bet is to simply replace the entire unit with a new one.
You could also just get a FloppyEmu. Those let you use SD card as storage and supports emulating hard-drives (or was it MicroSD card? I can't recall. I know the SCSI2SD adapter used MicroSD. I forget which one the FloppyEmu uses). It would save you the future trouble of replacing failing drives which will become quite common for such old hardware.
You won't be able to "open it up" and replace the drive with a SCSI drive. The 128k/512k did not have SCSI ports. The hard-drives at the time connected to the external floppy port. They are nothing like the external SCSI enclosures used on the Macintosh Plus and newer machines. The only other hard-drives you'll be able to use with it is other drives that also used the floppy port. I could be wrong since I never worked with these older machines, but I'm pretty sure the hard-drives at this time were not interchangeable. You wouldn't be able to use the enclosure for anything other then the exact drive that was in it. The controller board may have also been part of the main logic board of the drive it self, so that would also make it impossible to replace the drive in the enclosure with anything other then that exact drive. Unless you can cram a different brand/model hard-drive in there that also used the floppy port.
But such drives always came in an external enclosure (unlike the SCSI drives which also had internal versions) so that wouldn't make much sense and you won't really find them sold outside of the enclosures they came in. With the 128k/512k, your best bet is to simply replace the entire unit with a new one.
You could also just get a FloppyEmu. Those let you use SD card as storage and supports emulating hard-drives (or was it MicroSD card? I can't recall. I know the SCSI2SD adapter used MicroSD. I forget which one the FloppyEmu uses). It would save you the future trouble of replacing failing drives which will become quite common for such old hardware.