Been years since I've used 996, but it s definitely a stiffer tape, which can cause various tape path issues. When it was commonly used, I'd tension all my machines with it and all other tapes worked well. As for your questions:
1. Could be tension related or slitting related. Try a different reel.
2. Try another reel of 468 as a test. If noise goes away, it's tape related. Could be due to change in tension, as well as possibly needing a transport alignment. Also, clean / check tape path for any excess shed/oxide/residue.
3. flip the tape over and see if the problem moves to the other track. If so, you're dealing with slitting issues / edge damage. If problem stays on track 1, check tape path for alignment/stability issues.
4. Not really. every transport will have a different tensioning procedure. Best to follow the instructions in the service manual, unless you're very familiar with the correct procedure.
Dave Hecht