I recently purchased a second-hand A4000T (Amiga Technologies) and encountered this problem:
Using the diskdrive becomes impossible after a few minutes. The drive makes three "gronk" sounds like you get when you insert a faulty disk when in fact there is nothing wrong with the disks.
I've tried replacing the diskdrive with my A1200 internal one to no avail.
I find this problem disturbing and would really appreciate some help. Thanks.