Pop sound and vibration near firewall at highway speeds

Today I noticed a popping sound while cruising at highway speeds that I could feel at the firewall. It was kind of random and sounded like a very muffled backfire.

So what did I do immediately before that? I jacked up the car and rotated the tires. While doing that I also checked the front calipers for a noise that I had been hearing. A scraping after braking and during breaking while coming down an occasional very very large hill. As part of my exam, I pushed in the caliper pistons a little to be able to move the caliper and check for binding. All OK... Turns out I think it was a rusted dust shield. I pushed that back a little and the noise seems to be gone.

Not sure what this new highway noise is. Prius has 225K miles. 2007. I checked for loose plastic underneath and nothing apparent. At less than highway speeds it drives fine and is quiet on turns and while braking.

 

Just a follow up. The noise and bumping under my feet happened this morning on my way to work. A 10 mile drive where I am on the highway at 65 mph. After getting off the highway I drove another 4 or 5 miles with speeds below 50. No noise

on the drive back at noon it the same 10 mile highway run. This time nothing unusual. I am away from the car for the weekend but I plan on putting it up on ramps to see what’s going on when I return

 

I didn’t notice any dash lights or warnings with this latest issue

the car does have an issue while braking if I run over rough roads the traction light may come on and the brakes feel like the let go momentarily. Never found a solution to that. Been happening for years

 

Just drove up on ramps and nothing unusual stood out. I did notice it looks like my exhaust gasket is worn. I wonder if this could be the cause of my noises. I have had a cat efficiency code on and off and this would probably qualify as an exhaust leak although it’s not loud

 

Right. Gone is a better description I don’t have drivability or mpg issues yet so I would be surprised about the cat being clogged but who knows.

 

The gasket may be self healing because the car has been driving better than ever. I actually had some sounds that were like pinging under hardly aggressive driving prior to this incident. Drove 90 minutes on highway and hills, got 48.5 mpg.

Then when I was driving locally, the red triangle. I thought maybe a door open... but no. Damn I should have that scanner with me in the car. I noticed the air bag light on, check engine light on. I moved the car a few miles to another parking lot and got out to leave it there. Noticed a puddle below, went back and moved it back.. just water from A/C. moved back into the space. The triangle and check engine light were off. I was at a work site, so I got a ride to the hotel. Going to see if I can hookup a code reader in the morning.

Seems like with 225K and 15 years, it may be suffering from old age.

I haven't replaced the gasket yet because I have read reviews that no aftermarket gaskets will fit over the converter.

 

And the 95 mile ride home a day after was uneventful. No drivability issues, red triangles or CEL.