Help! Strange rattling sound at idle and with throttle in neutral 6s M/T

Ive got a strange rattling noise at idle. It comes and goes. I noticed the rpms will ramp up slightly and thats when it happens, then the rpms drop back down to standard idle levers. It will also happen when taking off in 1st gear, but only when it is cold. I live in seattle. It will happen when it sits out below 40 degrees. Once the car warms up, it does not happen. However, It will happen in conjunction with the throttle when in reverse.

Initially i thought it was my exhaust hitting the frame. (Ive got a stromung tucker). So I the tip back to create ample clearance and realized it was not the culprit.

After spending some time under the vehicle, I've isolated to the driver side cat. The heat shield above it does not make contact. I think it could be something inside the cat.

Has anyone ever encountered something like this?

Here is a video of the sound.

Strange rattling sound at idle intermittently. 2021 Tacoma Offroad 6 M/T - YouTube

 

How many miles ? Check if any rocks are on top of it when it’s cold . It doesn’t sound like a bad kat … sounds like metal on metal grinding check the radiator fan to see if it’s making any contact .also check the skid plate if u have one if it’s loose I can see this noise happening .

 

That sounds like a loose heat shield. Thin metal rattling against metal. Maybe the heat shield on top of the cat. I have see it when its the flange on the exhaust to a flex pipe or to a cat.

 

Just under 50k. I’ll check the radiator fan.
The reason I’m suspicious is because i checked the area and there is nowhere that metal is touching.

 

I had a baffle or similar come loose inside a catalytic converter on a different car. It sounded a lot like a loose heat shield and only occurred during a certain RPM range. Left it that way for several years because I didn’t want to replace the cat.

 

Figured it out.
A tiny pebble found its way into the cat heat shield. Was not metal on metal. It was ROCK