Knocking/popping when coasting and braking

I recently purchased a 2006 Prius with 206,000 miles in a private sale. I had a mechanic check it out before purchase and he thought everything looked good. But it appears the previous owner and their mechanic masked a lot of its problems going into that inspection.

Just to pass emissions for initial registration of the car, we had to get a new catalytic convertor and muffler. It was throwing all sorts of codes and the "new" hybrid battery seems to be very weak. They somehow tricked the TPMS to not illuminate for about 50 miles even though there wasn't a sensor present in that tire (I know this because that tire went flat at the tire stem and the person fixing it was surprised there was no tire pressure sensor inside. Based on what i've read, that would indicate shenanigans occurred).

There is a brake "creaking" issue as well. But I'll post that in a separate thread.


My question: when driving this lovely lemon around town (at less than 30 mph), there is a rattle/knocking/popping when coasting and braking. I sounds like it is coming from the front passenger side. Each pop happens anywhere from a couple times to upwards of a dozen times each time you let off the gas pedal. At very low speeds, like 5 mph, it doesn't seem to happen.

I tried to test whether going into neutral while moving helps. It seemed like it does. But it was tricky to get it to shift so I am not 100% sure that it does stop.

Here's the video:

I've tried to find solutions elsewhere in this forum. Someone with a similar issue thought it might be the engine mounts. I don't want to keep dumping money into this car. Can someone give me some good news?

 

Hi SFO. Thanks for the response.

You're right that it isn't tricky to get it into neutral. But timing it correctly the issue. It did seem to take a second or two to get into neutral but by then I wasn't able to definitively state whether going into neutral stopped the problem. Or if it stopped on its own before then. I will try some more experimenting tonight.

How would I go about doing this? Once the car is up, then what? Try to wiggling everything I see to see if something is loose?

 

I did some more tests. When I put the car into neutral while moving, it makes the sound about three times. When I keep it in drive, it does it a lot more times, like 10+. It also sounds sort of like something is beating on a percussion drum with a metal head on it.

 

The sound was something hanging down from my my catalytic convertor/exhaust and hitting the cat shield I had recently installed. (And two people sitting in the front seat exacerbated the problem.) Figured I'd post the resolution in case someone else experience a similar problem.