Hi so I have a jdm 2006 Lexus gs 350 and idk what’s going on with the transmission. Car was running fine throughout the day then I parked it for a couple hours and when I went to start it it started fine and when I put it into drive you hear a constant knocking not super loud but noticeably a knock please send input if anybody has anything or some ideas thank you

If you could give us more detail! So you started the car and its idling fine. Then once you put the vehicle in D it starts to make a noise. Are you still parked with the foot on the brake while in D? Or does the sound only come when you drive off? Does the knock sound go away or is it with you the whole time, is the sound change with rpm, meaning does it get louder when you raise the rpms?

Sorry about the lack of detail so all in the same day I was driving as I normally would throughout the day the car was running fine no odd noises or anything of the sort I got home parked the car for at least 2 hours or so and when I went to go back out I started the car sounds fine no issues and then I went to pull out of my stall foot on the break put it into D and it immediately started to make a knocking sound and the car was shaking at this point I didn’t even pull out of my stall and I went to put it back into P and the noise stopped. The car has not been touched since

What kind of a knock was it like an internal mechanical knock in the transmission or external loud knock like something vibrating on something. Im thinking maybe the transmission mount got damaged maybe and the transmission got pushed into the body. Or the bushing/guibo on the drive axle is bad. If you can take it to a mechanic shop just have him visually look things over. Once the car is in the air, It should be obvious to spot the issue, if the issue replicates itself at the shop.

But I doubt the transmission is bad, even if it is bad there are so many used transmissions as they hardly go bad in these cars. The prices for a used one is probably like 5-$800