My base 99 (4 cyl, 2wd, auto) has a very distinct rattle when I hit sharp speed bumps or potholes... it's done this since I bought it with 48k miles (I'll turn 100k within the next 2-3 weeks). There's a "flap" of metal inside the frame rail right behind the bumper that seems like it could be making the noise... it's hard to tell since I can't recreate the sound unless I'm driving (i.e. can't bang with hammer to make the same sound)...

Does anyone know what that "flap" is for? There's another flap in the pass. side frame rail too, but it doesn't seem to be as loose as the drvr side? I can't really get in there to get a good look w/o dropping at least the hitch, maybe the bumper too.

Any ideas?

Man I'm racking my brain to figure out what this could be. I took a look under my truck and I don't see anything that is loose or bolted on in a manner in which you are describing. Anyway you can take a pic and post it or email it (m.nevitt@gmail.com)?

I searched the TSB's and nothing applies. Weird.

Mike

Yeah, like AZRAIN said try and take a picture so we can see what the flap is you are talking about then maybe we can help you. It's kind of hard to figure out what you are talking about based on your description. I don't have anything like that on my base model '96. Nolan also has some pictures of the underside of his 2WD 4runner, look at his website and see if anything on there looks like what you are talking about:

http://members.cox.net/nolanlh/4runner_suspension_tires.htm

Check all the sway bar mounting points.

Check the exhaust system clearance all the way back. Pay special attension to the area at the cat and the frame cross member and where the pipe goes over the rear axle. If you have an aftermarket rear swaybar it may be clanking on the rear tail pipe flange and/or the pipe may be clanking on the rear axle trust link mount.

Gadget

www.GadgetOnline.com

do you have a tow hitch? i had a metal clanking before that turned out to be the "tow hitch shield."

If you have a hitch mount inserted into the rear receiver it will definitely rattle when you hit bumps....

When I'm not using mine I take it out and put a Warn shackle into the receiver as also shown in my front receiver mount..

I put several of the little adhesive rubber buttons or "feet" on both shackle mounts to keep them from rattling on bumps..

Thanks for the help and suggestions...

I'll try to clarify more, maybe I can take a pic tonight.
It is not the cat or anywhere along the exhaust nor any of the skid plates (those were my first suspects, 2.5 years and 50k miles ago)

I don't (yet) have anything aftermarket on the 'runner. The receiver is empty (no inserts right now) and tightly mounted (I checked all of the bolts).

Maybe I can explain the "flap" better:
Imagine that the bumper was removed; you can see down the length of the framerail, at least for a little ways. There is a ... hmmm ... strap(?) of metal, I'm guessing 3/4" - 1" wide and who knows how long (I can't see the mounting point).

Both sides (driver and passenger) have this flap, though on the pass. side it's kind of wedged against the wall of the frame rail so it doesn't rattle... the driver's side, however, is very springy; I can hold it down and let it "twang" back up, and I *think* that's the source of the rattle.

I'll try to take a pic of it tonight, but I'm not sure if I can get to where I can get a clear shot (I really don't want to drop the bumper and hitch, but I may have to).

Meanwhile I'll check around for some chassis links...

Ok, crawled under there again on my lunch break... There's a "spring loaded thingy" (that is visible in the bump-stop picture on Nolan's page that I was referred to above) that mounts to the track bar, and it looks like it is some sort of valve on the brake lines???

What is this? And how much play (lateral) should be there, and how strong should the spring be? This could very well be the source of the noise...

That sounds like the load sensing proportioning valve, I guess you don't have ABS? The arm is meant to move up and down freely.

No, no ABS... the spring is pretty light, so the arm moves pretty freely, but there's a lot of side-to-side play (along the pivot point)... Maybe this is just something I have to live with?