Last Thursday I started to hear a metal rattling sound coming from what seems like the Front passenger side. On July 22nd I had taken the tire off so I could have a easier time replacing the o2 sensor. Today I took the tire off and looked all over the place to see what could be loose but did not notice anything. Here is the sound. Any idea what it could be?

 

SOunds like loose heat shield on exhaust. Get under it with it parked engine off and parking brake set and whack the cats and wiggle any heat shields.

 

I agree, you probably tapped something loose when you did the O2 sensor.

 

Looked all over the exhaust and nothing was loose. But the sound disappeared once I got to 35-40mph. I was driving 25mph since it started and today once I got onto El Camino Real and went the higher speed it went away. Must have been maybe a rock. Hopefully that was it.

 

it is possible - ive had rocks get stuck between heatsheilds and exhaust compnents before and fall out days later

 

Or that wrench you put on the frame rail, lost a few tools that way.

 

Anytime I need a new windshield I just follow a mack truck out of one of the big diesel repair shops in town. Within a few miles a socket or a wrench will fly off the truck and smack my windshield. Bam! Free windsheild!