Diagnose scraping sound in car?

Factual Questions
1

Anybody want to guess what this car problem is? Sounds like a piece of heavy sheet metal scraping against something metallic, often loud enough you’d notice me driving by. Sometimes it squeels, sometimes it sounds more like a shovel on gravel, and occasionally it makes a slight clang. It happened for about 5 miles several weeks and several hundred miles ago, and then again (only the second time) minutes ago on a 2 mile trip. Seems to come from the front of the car. It is a variable sound with a rythmic component that is timed with the car’s speed (and not the engine speed if I rev that while coasting in neutral). I think the rythm is the same as wheel rotation. Turning the steering wheel a bit right and left changes it, and tapping the brakes a few times often quiets it, at least for a little while.

I can’t see anything amiss when I get down on the ground and look up around the front wheel suspension and wheel wells. I can’t feel anything funny around the tire. I can’t detect anything different about how the car drives and feels.

The car is a Scion XB, '06 model. I’ll see if the dealer can look at it this afternoon, but still wonder what it is and if it is very easy to fix, like some little guard or shield whose mounting nut just rattled off.

I can promise some thankful words and maybe local minor fame to anybody who can figure it out for me.

2

You sure you don’t need new brake pads?

Brake pads often have a little indicator strip that drags on the disc (or drum?) if the pad gets too low - specifically as an annoying reminder that it’s time to replace them. Usually this is more like a very high-pitched metal squeal.

3

Or a loose heat shield, or plastic air-baffle, or loose exhaust system clamps…
Lots of things can cause a noise like that, hard to tell what, unless you can localize it better.

4

I think I had something similar.
Sounds like scraping metal that is very damaging to the car.

I took it to my friend who found the issue to be rusty brake rotors. A small loose chunk of metal fell into the rotor inside and was scraping along the sides when driving. It was more pronounced when turning right because it would cause the metal chunk to touch more I guess.

He had to take apart the whole front wheels to see that it was inside the rotor.

5

Thanks.

md2000, it doesn’t sound like the brake pad warning. This only happened the two times I describe, quite loud and distinct, with absolutely nothing in between. It is more variable and deeper than the brake pad warnings, too. Plus, don’t brake pad warnings whine especially when you are using the brakes? This either ignores the brakes or improves for a few seconds when pumping them gently. Also, I don’t happen to know whether this model car uses those.

Khendrask, yes, I picture things like you list. And I wish I could localize it better.

Canadiankorean, this sounds close. But, if by “scraping metal that is very damaging to the car” you mean it sounds like large, expensive parts scraping each other, I think not. It sounds to me like one part is sturdy sheet metal, like the blade of a trowell or small shovel, and the other part is heavier and not contributing much of its own sound, like a brake rotor or a driveshaft. Though, this car doesn’t have a driveshaft going to the back wheels, only the short shafts between the transmission and differential assembly to the front wheel universal joints.

If there were a cover or a heat shield or splash guard, something like that, maybe attached to the brake caliper, and it was able to flop over into the wrong position so that it barely grazed a brake rotor, I think it would sound this way.

More info, though not much help - I spent over an hour at the dealership, and they drove it (which as in all but two of my driving experiences didn’t make any funny noise) and inspected it on a lift (four different guys). They found nothing. They did not, however, pull the front wheels off, which for no very good or experienced reason I was hoping they would. Then I drove it around their parking lot with one of them, and several times parked it, setting the brake, and then backed out of the parking space while turning left, stopping, and driving forward. I think this was the move I made immediately before hearing it in both of my experiences (as well as a few times a day without any noise). We heard nothing.

So, it does this thing that is loud enough to be embarrassing, but so rarely nobody can find it.

6

OK, I found a web site describing replacing front brake pads on my car, here:

http://www.clubxb.com/forums/f18/diy-front-brakes-any-disk-brakes-31253.html

There is a black sheet metal stamping that covers the side of the rotor toward the middle of the car, with a patch of yellow at its highest part. It is especially visible in his 13th photo, though easy enough to see in many of the photos.

I swear, this sounds just like that cover would if it were loose. Or, maybe, if there were something caught in it so it could sometimes rub against the rotor, like canadiankorean describes. I think this chunk of metal looks like it would make the noise I heard.

Oh, it does also say this brake uses the squeeling tab warning, but I still don’t think that could be it.

7

I can bang and rub against that black metal stamping, and it sounds much like the noise. But neither of the two is loose, so it would have to be something else maybe wedged or caught in the space between this and the rotor. At least, that is sure how it seems right now.

8

Sounds like it could be the wheel bearings.

9

It didn’t sound very damaging like metal was being ripped apart.
But it definitely didn’t sound small.
It sounded like grinding that if left uncheck would damage the car.

My friend did say that it really wouldn’t damage the car in anyway.

When I took it to my friend at first, he couldn’t figure it out. THe sound was somewhat random and only happens when driving. So I drove it close to him while he tried to listen where it was coming from. That day, he check the brake pads and saw nothing unusual. He said that it might be rusty parts but normally rusty parts wouldn’t make that sound.
I came back a week later because the sound was almost constant.
He decided to take apart the front brake system. When he took apart the front rotors (the thing the brake pads hold), he noticed it was very rusty. Then he looked inside and found a chuck of rusted metal about the size of a peanut. He machined the rotors to get rid of all the rust.
After that no more metal grinding sound.

10

Maybe it’s the man with a hook for a hand!

11

Canadiankorean, I think what you are describing sounds pretty likely as my problem. So, it didn’t sound to me like really big parts grinding against each other, but as you say, it didn’t sound small, and sounded like if left unchecked would damage the car. I don’t see what car part can be shifting out of place, but I can definitely imagine a chunk of rusted metal about the size of a peanut. I think it’s usually lying over here on this side, but sometimes gets bumped over there where it interferes with the rotor or hub turning by being jammed against this black cover, and transmitting sound to it. Now I am trying to figure out if there is a way I can look in there without pulling the wheels off, as I don’t have a proper jack and my driveway is a bit muddy for rolling around on. I have one of those pipe inspection cameras with a long gooseneck - maybe I can spot something with that.

Autolycus, yes, that’s nice, thank you very much. I actually think the wheel bearings squealing for five miles and then shutting up for a thousand would be a better hypothesis. So next you are going to tell me the guy said his daughter died ten years ago and the call came from inside the house, right?

12

I heard that story but the hook was on his foot.
What movie?

13

And he knows what you did last summer. Dirty.

14

Pull your wheels and check for a rock stuck in the braking system, may have to pull the front brake calipers off and take off the rotors to find it/get rid of it.