Tried to recreate the issue but can't. Both times this occurred while creeping in 5pm traffic jam traveling less than 10 mph. Not sure if its some type of unplanned detonation, on the first incident it was severe enough to make me think I was hit by a vehicle. Never experienced anything like this from fords, jeeps, chevys, hondas, and previous fj, tacoma, and 4runner. Not sure if an electrical interference, gases in intake due to engine design cycle, or engine to torque converter issues. Toyota has assigned a file number and told me to get it to a dealer. No codes flashing.