All the above comments, lol you guys should try better to stay current with the issues on these cars. This issue has been covered multiple times and should be well-known by now!
It's the electric power steering coupler. It makes corrections over bumps and rough pavement, and rattles if it has a broken part. The power steering behind your steering wheel has a worn or shredded bushing, a $20 replacement part.
Here's the repair procedure for the 86 / FR-S / BRZ EPS electric power steering coupler:
https://www.ft86club.com/forums/showthread.php?t=133606