B737 MAX Captain reported a flight control malfunction.

Narrative

While in cruise at FL340 and approaching the fix ZZZZZ with the autopilot (A/P) on; there was a slight turn in our route. As the A/P started the turn; the roll commanded by the A/P continued to steepen; up to 30° AOB (Angle of Bank) as the yoke was turning in the opposite direction to arrest the roll. Simultaneously we felt and heard a low rumble/flutter that we initially attributed to light turbulence. I noticed and commented aloud asking what the A/P was doing. I had put my hands on the controls as the 737 MAX annunciated audibly as well as on the Primary Flight Display (PFD) 'ROLL AUTHORITY ROLL AUTHORITY'. At this point the Autopilot disconnected (I am unsure if I reflexively did this or the A/P disconnected due to the ROLL AUTHORITY limit). I counteracted the roll with additional yoke input; as well as initiated a shallow descent. I told the PM to inform ATC of our altitude deviation; and he complied adding that we were dealing with a flight control malfunction. At this point the roll had subsided and we returned to normal flight. I gingerly re-engaged the A/P; initially thinking we had hit wake turbulence. We felt/heard the flutter and low rumble a couple of more times in flight. I now believe we had an asymmetric spoiler deployment; which would explain the flutter and uncommanded roll. Cruise FL340Mach .75 (approx 255 kts indicated/435 TAS)Approximately 155k pounds (we had recently sent for landing data)Approximately 20 miles in trail of a 737; same altitude40 kt direct headwindTotal time of event approx 1 min