I had an identical problem a month ago.
In my A4000T, I currently have a 80Gb Quantum IDE drive which has been OK, but sometimes makes really dodgy sounding "grinding" noises at times.
It's been doing it for ages, though I eventually decided to do something about it.
So I bought a new replacement Hitachi (IBM) 80Gb drive and found exactly what you have with scsi.device 43.43.
If I use the original OS3.9 scsi.device, it works without any problems.
The current solution was to copy all my data to the new Hitachi drive and keep it as a working backup. The original Quantum drive is still in use. It runs 24/7.
I'm sure there's some kind of compatibility issue with scsi.device 43.43 and certain IDE drives.
The easiest short term workaround is to go back to using OS3.9 without BB2 (not sure if scsi.device from BB1 has the problem), or to try another IDE drive from a different manufacturer. Quantum seem OK, but as we now know, Seagate, Hitachi/IBM drives seem to have a problem.
Any other suggestions welcome.