When our '08 Toyota 4Runner is put into R or D for the first time on any day — summer or winter — there’s a conspicuous continuous knocking sound for the first 30 - 60 seconds or so. Putting it into neutral ends the knocking. As the vehicle warms up, the knocking goes away.
The dealer’s shop has no idea what it is.
The vehicle has about 26K on it. We bought it used and have had it for about a year.