Annoying rattling noise!!

For the past few months I've been hearing a high-pitched noise coming from underneath my truck. The general area is coming from my back passenger side tire.
I was rear-ended not too long ago, but I believe it may have made the noise before that, and didn't bother me too much then.
The noise is most intense when I let off the gas at any given speed, but stops for the most part or isn't as loud when I brake or accelerate. It sounds as if something may be loose. Just the most irritating sound. Can't tell if it's a rotating sound or a back and forth one. Given I know next to nothing about what could be wrong with it I had my older brother check it out and he couldn't find anything. It runs perfectly fine, just the noise is incredibly annoying. Only work done to it was a 2 in level on the front and a replaced bumper. Brake pads and belts are new as well. Anyone know what it could be? I'm clueless! It's a 2002 prerunner Tacoma

 

Very possibly the guts in your catalytic converter have broken up and are now rattling around inside of it. That's what happened to mine and it still does it but I've gotten used to it for the time being until I put a new exhaust under it. Easiest way to tell is crawl under there with a hammer and tap both the cats and see if you hear the rattle and if they rattle well there's your problem.

 

This is where I'd start on this as well. Sounds like pennies or rocks on metal when the cat breaks up.

 

suspension squeak? check for something on the rear drum that's rubbing?

 

@2004TacomaSR5 i will attempt to see if that's the problem. I've mainly heard exhaust so far so that could be it. Thank you so much!
@Aw9d @frizzman ill try and take yalls advice. I'll let y'all know if that's the issue. Thanks again!