Jumping in on this thread as I now have developed this 'seagull noise'. I had multiple factors I am considering, but this thread gave me some to think about. The noise developed after a service (trans fluid, tire rotation, alignment, sparkplugs and oil change). I did have the window rain guard on the passenger side (not sure if its making a noise from that).
Under my inspection I notice the wastegate actuator is a little loose. I can move it side to side a small amount. I also noticed I can wiggle the driveshaft near the center bearing.