Mysterious rattle only with pressure on gas pedal

Hey all!

Go easy on me -- I'm new to actually working on my own vehicle, and I'm absorbing all of the information I can, and have researched this for weeks now.

Have a 2000 4runner SR5, 4WD. about 251100 miles.

Having that said -- I've had this annoying as f**k rattling noise coming from the front passenger tire area for about a year. When it showed up, I checked it out with my father (most reliable mechanic I know, maybe I'm biased) and we determined it sounded like it was coming from the hub/caliper itself. It was very low, and sounded metallic, like a tiny rock in a tin can. No rattling feeling at all. Just a sound. Other people could barely even hear it when I asked them to listen for it.

At that time my check engine light began coming on randomly, then turning off after a few days. We checked the catalytic converter and heard no rattling. I ended up getting my transmission serviced later that year with my regular mechanic in CA, I forget exactly what code was read at the time. But it was not the cat, and it was fixed after that. I passed emissions in California in December -- but failed only bc of the damn sensors needing to reset, so I had to smog again when I went back to Utah in January and passed safety AND emissions with no problems. All that back story to reiterate the reasons why I don't think it is the cat.

FF to moving to Vegas, where I am now -- I got new tires/alignment recently and the rattle became louder than it has been for the entire year it's been there. I forgot to ask the mechanic to check it out. Went to get new rotors because mine were warped to shit and asked another mechanic to please inspect the hub for me as it was still suspect.
This guy instead tried to tell me it was my strut mounts and sway bar links/bushings (his exact words were that the bushings were rotted) and wanted another $1000 out of me to fix it right then. I told him to just put on my new rotors and brakes and I would check it out myself.

I crawled underneath the truck and inspected my sway bar links/bushings and strut mounts (strut mounts were harder to inspect, admittedly), took photos and video to get 2nd/3rd/4th opinions from other mechanic friends -- and determined they are fine. Also not causing the rattle. I did have a deep metallic klunk noise on the front driver side for about a week when braking at lower speeds, which couldve been the strut mounts, but that went away when the rotors were replaced.

Since it got louder, it now echoes all the way to the drivers side, I can hear it with only my window down. It sounds like a bad cat. No doubt in my mind that is the exact same kind of noise. It sounds like tiny rocks or a dime rattling around in a very thin tin can.
But it only happens when my foot presses on the gas, and it increases in intensity the harder I am pushing on it. It also ONLY happens when I am moving. If I'm in neutral or park, nothing at all. If it were the cat -- it would be rattling under these conditions, too -- correct? Also no symptoms of the cat being bad aside from the check engine light coming on briefly a few weeks ago. I took it to get an autozone to read the code and the dude just turned it off -- so I never got an answer, if it was a false alarm or if it was important.

I checked the heat shields and didnt find any that felt loose. My only other idea is that when I was inspecting the cat yesterday (knocked on it and felt no rattle), I did notice that the gap between the heat shields had some small rocks stuck in it. I have taken her into the mojave desert many times on dirt roads. So is it possible that these rocks may have gotten inside the shield?

again -- I am new to the self-repair world, and also sick of having to wade through asshole thief mechanics to find the ones who wont try to screw me around. So any suggestions are very appreciated, I just want to figure out what the hell this is so I can either fix it or pay someone to fix it, if I am not capable.

So thanks in advance to anyone that can give me a direction to try here!

 

perhaps a cracked drive plate, flywheel to most, but at the Toyota parts counter that's what it's called.

 

I had a heat shield on the exhaust on my '99 make a similar noise. You can either get the piece welded back together or do a good ole farm boy hack and use wire to tie it tight and keep it from rattling.

 

Mine does the same thing I’m boggled I’ve looked everywhere. Sounds like metal rattleing at start up and when you slowly accelerate .