125k miles on a Gen 2. Just replaced cat (that's what the p0420 code is). For the last week or two I noticed over 60mph a little clinking feel in the accelerator and audibly. This morning when I drove, there is a louder clicking/knocking whenever I let off the gas. Also when moving at like 1-2 mph the click/knock is present. Mechanic did a visual inspection and couldn't identify anything, but said it should be safe to drive until tomorrow when he has availability. I've been a lurker here for a long time, but just made an account today so I can't post links to videos with audio fo this unfortunately. I can try to DM the YT links if that helps!
You can find links to two videos on reddit. r/prius. It's a new thread titled (Knocking / clicking after letting off accelerator. (2009)
That could be. When I got my MillerCat shield installed, I immediately noticed that a small rattle that I heard previously had disappeared completely and the car was noticeably quieter. The rubber bushings on the exhaust were relatively new from before when the cat was replaced by prior owner after a theft, so that wasn’t it. Everything now is tight and quiet.
Mechanic said the struts and control arms need to be replaced. That kind of adds up with some of the clues I've gotten as to whats wrong. Steering seems to shift sometimes on the highway, the clicking increases when I pull the steering wheel slightly right. Will know today if that fixes the issue.