I don't know much about it, but I think BenganJ would say something like this.
"I'm sorry, but for AA 4x, 1650 is unpowered and unavoidable."
BenganJ was limiting even the higher end 1660Ti to 30fps. I also used to limit myself to 30fps or 40fps when I had a 1070.
I would suggest reducing the density of the grass and trees and changing the shadow settings back to 4096.
Or use 2x, although the quality of AA will drop. Furthermore, if you use DSR with 2x, you will get slightly better results with AA. (Instructions can be found on page 1 of this thread)
Also, in places where the fps drops, the blinker sound can be slower or faster as you say.
Sorry for my bad English.