I have been hearing a metallic rattling/clanging sound from under my truck for at least 4 years. It only happens while moving, not while stopped (either idling or revving the motor). I hear it at between 2600-3000 rpm in 1st, 2nd or 3rd gear or when letting off the gas while still in gear. I just noticed this last week that it rattles while coasting in neutral and revving the motor, too. Took it to a mechanic friend's shop a couple of years ago, put it up on the rack and accelerated in 1st gear. It sounded like the rattle was coming from the leaf springs. At least that was his theory. I made some teflon shims and inserted them in a couple of spots (one of the plastic silencers was missing) and sprayed white lithium in the bushing and between the springs. Didn’t help. I then put it up on frame stands myself and accelerated in first gear. The sound was quite evident at 2600 rpms and putting a piece of hose to my ear to pinpoint the sound, it sounded like it was coming from the middle of the driveshaft (regular cab, single piece driveshaft, no carrier bearing). A weird spot for the sound to occur and the driveshaft is newly rebuilt with new u-joints. My mechanic thought the driveshaft was just making noise because my truck was up on framestands and the back wheels were hanging low, leaving the driveshaft at a pretty sharp angle. Lubed up the driveshaft, just to be sure the slip yoke wasn't dry. Still rattling.
So, I took it to another mechanic. He seemed certain it was the catalytic converter and the plate that protects it from road hazards. He squeezed/tightened the tabs that connect the protector to the converter and bent it away from the converter in a couple of places. I think the rattle decreased, but it might be wishful thinking. Anyway, if it was the converter I would think it would happen when the truck is stopped and I rev the engine. The rattle only happens when the truck is moving. I tried to remove the protector, but it was difficult to bend up the tabs and I suspect they are spot welded to the converter. I did read about people putting a big hose clamp around the whole assembly and tightening it down to eliminate rattles.
Stumped. Any ideas?

1998 Tacoma 4WD, 2.7l 4 cyl, 5spd, Reg cab

 

I'm thinking the exhaust somewhere...Might be up a bit higher, there are clamps, I think, that are coming down the down pipe. Check to make sure all the heat shields on the body are tight.

 

check the rear shock cover things, thats were mine was rattleing

 

X2, There's a clamp on the down pipe that should clamp the exhaust to the a bracket on the transmission. Passenger side.
Check that.

 

4runner114:
Could you elaborate on 'rear shock cover things'? I am not sure what you mean. Maybe it is different on the 4runner and Tacoma?

 

Scuba:
I removed and re-installed that clamp when I put a new motor in recently. I think it is tight
Lumpy:
Do the heat shield trace the path of the exhaust on the underside of the body?

 

Also, does it make sense for the exhaust components/heat shields to rattle just when the car is moving?

 

Update: I heard a very slight rattle when revving the motor at a stoplight. So the truck does not have to be moving for rattle to occur. Also, secured the cat converter with 2 big hose clamps. No improvement. Banged away underneath with a mallet. A few suspicious areas, but nothing that could account for rattle. All heat shields seems tight.

 

may i ask, how loud is the rattle? Do you have to pay close attention to notice the sound or is it really noticeable? Sorry i just had to ask this.

 

With the rear slider window open, it is pretty noticeable at certain rpm's. With the slider closed, it is pretty faint. I hear it, but no one else does

 

I am really starting to think it is the driveshaft. I put it up on framestands tonight and listened underneath while my neighbor "drove". It just has a hollow metallic pinging rattle, the same frequency as when you hit the shaft with a mallet. Heat shield sheet metal rattle wouldn't be as pingy. This is really bedeviling me

 

i had the same thing !! it is the head shield around the cat conv. start her up in the morning and climb under there real quick and start to hold and release the cat before it warms up you will see the heat shield vibrates !!!!!!!!

 

Mick: Is it the heat shield that protects the underside of the body from the exhaust heat (above cat converter) or the protective shield that is under the cat converter that was rattling for you? The underside shield has holes in it and it used for protecting the cat from road hazards

 

MINE was the protective cover on the bottom of the cat drove me nuts for months
sounded like my drive shaft was about to fall out i was able to drill a few small holes in it and used a brazing torch and rod to stick them back togher stopped that annoying rattle watch ur cat too they steal those like crazy !!!!