If you do find it to be the rear ACCT causing your issue, then I personally suggest moving over to MCCTs if possible. I think it's fairly universally accepted around here as a good mod.
Without them I would have never heard the knock from the bad balance dampers (they made the engine so quiet). I feel they saved my engine at this stage, lol. I grabbed mine from TOC, but there are a few manufacturers out there.
1986 Kawasaki Vulcan 750
NGK Iridium Plugs #7803/DPR7EIX-9
Duralast Gold ETX15 AGM Battery
Coastered & Shaved
Metzeler ME880 [110/90-19, 170/80-15]
Balance Dampers Replaced
Rebuilt Forks w/ Progressive Springs
VN750.com Grill Cover
Emgo 23-92411 Handlebars
MOSFET FH012AA R/R
1990 Kawasaki Vulcan 750
1998 Honda VFR800 FI
2014 Honda VFR800F
1989 Pontiac Firebird Formula 350