Re: Armalite AR-10 S.A.S.S. free float handguard wiggl
New rifle or used?
If new contact Armalite, if not I would breakdown the upper and inspect everything. Assuming correct assembly given your description I would hold the OD threads on the barrel nut and ID threads of the forearm suspect.
Just because the barrel seems tight that doesn't mean it is. The barrel could have been Loctited into the receiver but the barrel nut was just hand tightened.
You won't know until it is broken down and inspected.
Although I have not dealt with a 10 with this issue I have seen AR15's that were dropped or otherwise mishandled that had enough pressure put on the fore end to distort/bell the receiver end of the tube. However those were also lower teir forends such as UTG and such.