My 2007 GX470 is making a clunk/thud noise when braking (more often when braking hard or on a downhill slope) and then again when I let off the brakes and start to accelerate. It is significant enough that I can feel the car jerk some when it happens, almost as if someone has tapped the back with their car. Any thoughts on what it could be?

 

This is a known issue and can be repaired under warranty. See first sticky post in this forum.

 

Yes, see sticky at the beginning of this forum.
Most likely, the noise is coming from the drive shaft.

I fixed mine by simply using good quality grease and a grease gun. Check amazon.

See this for more details. Properly lubricating the drive shaft will fix your problem.
https://www.clublexus.com/forums/gx-...riveshaft.html