Nick, I agree BNF/RPM is one possible cause (as it is a bit close for comfort) but we can’t do too much about that now – it’s been running for 25 years like this. We have to typically re-torque every 3 months and it occurs across all fans (young and old).
We’ve found that it becomes worse with windy stretches which is kind of expected but I was just wondering if this is common among other users.
