Yes, we have turned off the unit's operation to verify that the problem cleared up. I have no idea how long the problem has actually been there, they just commented on it one day while I was out in the back area with the doors open as they were reconnecting some box cars down the track.
I'm getting the consensus that it could be ski shine at the edge of the building which is where the top of the vault is. It's an Aluminum roof and we've had that area repaired several times over the years due to ski shine.
This particular unit is designed for 5Me but we never run it over 2.5Mev
I will be checking with a Rad monitor some time this week to verify the strength. We may need to raise the height of the concrete wall around the top of the T-section of the Beam tube..