What could that be knocking in my car?

February 11, 2009 12:39 PM

Nissan Altima filter: I have a '97 Altima. There is a noise coming from(I believe) the rear left tire.

It seems to be a knocking when driving normal speeds and more of a scratching at lower speeds(~20 and under). It also seems to be more pronounced at the lower speed. Though this may just be due to the lack of engine/wind through the windows noise. I'm pretty sure it goes away when I apply the brake Any ideas? I'm going to take it to be checked out, but would like to have some ideas going in. I'm a girl and look like I'm 15 years old, so being able to say "I think it's xyz". I just don't want to chance being told "you need a new rear axle", when it's actually something simple. Thank you! Also, I plan on posting to some Nissan forums, but wanted to spread my net wider.

posted by Epsilon-minus semi moron to travel & transportation (11 comments total)

It might be just a rock banging around behind the brake shield.
posted by Harald74 at 12:56 PM on February 11

Eh, that is if your Altima has rear disc brakes... The brake shield is a metal plate on the inside of the brake disc, and it's supposed to keep crud of your brake system, but sometimes it just traps it instead.
posted by Harald74 at 12:58 PM on February 11

I had a broken wheel bearing on my '95 Toyota Corolla last year (also rear left wheel, coincidentally). It made more of a muffled "whump whump whump" that varied in frequency with my speed. It may not be your issue, but it is another thing to ask about.
posted by sararah at 1:05 PM on February 11

I had a 97 Altima with a knocking from the back tire area. Turns out the tires were terribly cupped and the thump thump thump was because of this. It was louder at lower speeds; on the highway it wasn't as noticeable.
posted by villain extraordinaire at 1:14 PM on February 11

villain..by "cupped" do you mean the way the tire fits on the car?
posted by Epsilon-minus semi moron at 1:24 PM on February 11

Bad wheel bearing.
Tip: Always replace wheel bearings in pairs, or else very likely you'll hear the other wheel going bad soon, too.
posted by artdrectr at 1:29 PM on February 11

Any of the above, or simply worn out brakes. I'm thinking this because you talk about scratching at low speeds and thumping at high speeds, and going away when you apply the brakes. That's what my (Volvo) brakes do when they go past their date, which in nasty gravel-y and slushy Sweden happens all the time.
Its a routine thing, brakes - they do wear out and make the funniest noises, especially when you happen to be far from home.
Stay in the shop until they've cranked up the car so you can see it's not the rear axle. But honestly, if it's brakes, a car repair man would be pretty stupid to suggest something else, 'cause you can easily get a second opinion.

(Seconding the wheel bearings in pairs replacement comment. IF that's the trouble)
posted by Namlit at 3:22 PM on February 11

Could be brakes, could be bearings, could be tire, could be bushings or sub-frame or struts. Really, it could be a large number of things. Pretty impossible to diagnose with just a description of a sound. We won't be much help.

Cupping from the Car Talk web-site:

If the struts are really bad, the tires can literally bounce up and down like a basketball....badaboom... badaboom...badaboom... badaboom. And each time the tires hit the ground, a little bit of the rubber gets scraped off. Eventually, you get a lot these little scuffed spots, and that's called "cupping." And as you know, cupped tires make a lot of noise. It sounds as if a cement truck is on your tail.

But, if you take it to a decent place, you can get an estimate and take that information to the forums and get some better answers. That's what I would do.
posted by luckypozzo at 6:44 PM on February 11

take it to a decent place, you can get an estimate and take that information to the forums and get some better answers

Seconding. Also, if you're worried about the girl bias, get the first quote, then take it to a second place and get a second quote. Don't tell the second place what the first place said. Compare the two quotes, and check out the forums.

I have to say, the "girl bias" has grown much less in my 20+years of driving -- or maybe theyb just don't bother trying it on an old lady like me. Anyway, I still go in expecting and I find my fears are overblown. Car problems are empirical. Just learn to ask "How do you know?" and to say "Show me the problem" and to ask "Is there anything else that can cause that?" As long as you aren't just passively accepting the diagnosis, but insisting on some evidence, you can be reasonably confident of fair treatment.

these days, the bigger issue in car servicing seems to be that people who evidently have money are exploited for all the little jobs. If you're worried about the final bill, just say up front "I'm concerned about basic maintenance for safety, not optimum maintenance. What's the minimum I can do to stay on the road safely and pass inspection?" They'll catch on that you're not a cash cow and stop recommending the long, long list of dealer-recommended jobs.

That's general advice because I don't know your specific problem, but as a woman who oversees her own auto maintenance, those are a few approaches I've learned to do. The main thing - don't be intimidated, and don't authorize any job you're not completely convinced you need. There will always be another mechanic who'll work with you.
posted by Miko at 8:06 PM on February 11

I had this happen on the right side of my car, mainly when I braked, but always when I went down a particular ramp. A month later my muffler fell off. Turns out it was loose and when I braked it dipped (until it fell off). It happened to me at what seemed like lower speeds, turns out it was just noticeable because lower speeds meant I was on residential streets with stop lights and turns all things triggering the muffler dip. I am not a mechanic or mechanically inclined.
posted by syntheticfaith at 6:22 AM on February 12

As I understand it, cupped tires are caused by bad struts that cause tread depth to undulate unevenly. They said I could drive on it with no problem, but boy was it annoying.
posted by villain extraordinaire at 8:31 AM on February 12