I agree with
@Munchkin here. I've tested many floppy disks lately and I've experienced that horrible sound on a few of them. I used a cleaning disk with fluid in the drive afterwards just in case. So there is a chance there are a few dirty and dodgy disks causing the drive to malfunction when it tries to read them.
If diagnosis can be done via AmigaTestkit, I can write an ADF to floppy and send it to you in the mail, but I live in Norway so might take some time before it arrives.
Please send me a PM if interested and I can fix it for you.
