Rattle noise when decelerating

[Boule]

It's an 07 with 20k on it.

If I'm running at medium to high rpms and I decelerate, by downshifting or just lifting my foot from the gas, I hear some rattle noise that seems to be coming from the back.

I've been looking up the issue, and I saw it's fairly common in 00 and 01 cars, and they even have a TSB for that. But I didn't find anything related to newer cars.

Mine is still under warranty. Any ideas what's the problem (if any) ? Should I take it to a dealer for that ?

[starchland]

from the back eh? hmm. does it do it in every gear? what about in neutral no load on the engine? Why not take it in if it bothers you and its under warranty. mileage on diff fluid?

[Coop]

I have an 08 CR, that I get some from the transmission/gear shift sometimes. Seems to be nature of the beast.

[repiv]

I doubt that you have the typical AP1 clutch deceleration buzz, but you just never know. The thing is, this buzzing should be coming from under your radio (about where the clutch would be). A rattle that originates from the rear is another matter, unless of course, you are having difficulty in homing in on the noise. Being that yours is such a new car, I'm inclined to think that you have one part of the car vibrating and hitting another part of the car. In particular, the exhaust system might be hitting a heat shield or some other portion the the car's underbody. When you decelerate, lots of harmonics can develop within the car and some of it manifests itself far from where the harmonics begin. Exhaust systems tend to vibrate the most when just initially taking off but can also reach a significant amplitude during deceleration.
Off hand, I would suggest you have the dealer look at it unless they are going to charge you big money just to take a look. They may just end up saying they can't find it and charge you for the experience. However, if they do find it, they should fix it for free while it's still under the 3 year factory warranty.
Before you get too ambitious, make sure your spare tire tie down is securely screwed on and nothing back there is loose. Also consider that it might be your passenger seat back that is too reclined and it's bouncing off the back wall. Also make sure it isn't your passenger seat belt rubbing on something when the car vibrates and bounces down the road.
If you are adventurous and want to play with it yourself, I would suggest you go to the back of the car (it doesn't have to be running) and grab one exhaust tip at a time and jiggle it vigorously. You may be able to duplicate the sound. If this doesn't bring any results, I suggest you jack up the car from the right side (mainly because most of the movable bits are better accessed on that side), use a jackstand for safely and have the ebrake firmly applied and leave it in gear. Crawl underneath and with a gloved hand, start thumping on everything you see under there. Go the whole length of the exhaust system. Thump the propshaft and the 1/2 shafts. Give each tire a good punch. Don't hurt yourself. You'd be surprised at what you might discover.
If you find the offending object, then you can begin to figure out how to fix it. You might have to bend a heatshield more out of the way or change the exhaust hangers just a little bit to make better clearance or you may then know you'll need the dealer to do something about it under warranty.

[Boule]

To answer some of the questions:

It does it in pretty much every gear (never happened in 5-6, but I'm never really in high rpms at those gears). It also happen when I downshift while blipping the throttle (heel and toe)
It doesn't do it in neutral.

Repiv:
I'm not adventurous :) and I have to admit, I don't know enough about cars to be comfortable in messing around. I'll definitely check if there is something loose, like the spare tire, the exhaust and the passenger seat. Otherwise, it looks like I'm going to a dealer.

Any particular dealer recommendation in the bay area ?

[repiv]

It seems to me that it doesn't matter what gear. It's purely dependent upon road speed and thus, my conclusion that it has to be from the output side of the tranny to the wheels.
As for a shop in the Bay Area, you should post that question up in the Bay Area forum. I'm in Canada.

[Boule]

I checked the spare tire, it seems to be tightly in place.
I also tried to jiggle the exhaust tips, they barely moved, without any noise resembling the rattle.

Looks like I'm heading to a dealer...

[Boule]

A little update on this:
I mainly hear that rattle in 2nd, 3rd and a little on 4th gear. RPM's don't need to be very high, I can reproduce it fine around 3-4k, at 25-35mph.

Anyways, I had a tech (who seemed quite knowledgeable about s2ks) take a ride with me. He said the rattle is "normal, it's the drivetrain jerking when the car decelerates"

Good enough for me to let it go ?

[Jasonoff]

The reverse spring in the shifter will make a ringing sound during deceleration if there's not enough grease in there.

[Boule]

It's the worse trying to say "how it sounds like". It doesn't sound like a ringing noise though.
Also if it cam from the shifter, I should be able to tell where it comes from pretty easily, right ? It doesn't seem to be that close to me...

I'm not too convinced about that "drivetrain jerking when decelerating" explanation though. Why would it happen at 25mph and not at 50+ or at higher gears in the same rpm range ?

[repiv]

I also tried to jiggle the exhaust tips, they barely moved, without any noise resembling the rattle.
Do you have the stock exhaust? Jiggling it may not reveal much when the car is just sitting there. You have to slap it to get it to vibrate if that's what it is. Put a glove, go under the side of the car and slap a muffler from side to side.

[Boule]

Exhausts are stock.

I did slap them, not to hard though, I don't want to hurt the car :o
I will try to check out the mufflers and see what happens...

[repiv]

Exhausts are stock.

I did slap them, not to hard though, I don't want to hurt the car :o
I will try to check out the mufflers and see what happens...

OK, the stock exhaust is not known to rattle, however, sometimes the cat can have the internal discs disintegrate. Try slapping it.

[Jasonoff]

Also if it cam from the shifter, I should be able to tell where it comes from pretty easily, right ? It doesn't seem to be that close to me...Nope. It's almost impossible to pinpoint where it's coming from.

Push down on the shifter when you hear the sound and it goes away it's the revers spring. If not then keep hunting :)

[Boule]

Pushing down the lever didn't make it go away... Still on the hunt :(

I tried slapping the mufflers, didn't hear anything unusual. I didn't get around to try the cat (damn this car is low !), BUT... I have a video :D

http://www.youtube.com/watch?v=aQUAFiZ6mR8

You can hear the rattle distinctly at 25-26 seconds, and again at 35-36 seconds. I'm in 2nd gear and letting go of the throttle pedal.

I really hope this helps !!

[repiv]

That's sound like drivetrain backlash noise. This is all the normal spaces between gear teeth and shaft splines, clutch disc springs moving from one end of their travel to the other when you decelerate or accelerate. There are spaces in the tranny, diff, CV joints. When you accelerate, all the spaces get taken up in one direction. When you then decelerate, the forces go backwards upstream in the drivetrain and spaces get taken up on the opposite faces of contact. Clutch springs compress and decompress and compress back up in the opposite direction. Like your tech said, it's probably normal and he had the advantage of being there. We're not going to be able to diagnose it any better than him. I think you're obsessing over it too much. If it gets worse with time, get the tech to listen to it again. Till then don't worry about it. All cars make these noises. In the S2000, you can simply hear them all because of so little noise dampening and insulation.

[Boule]

I see, thanks for the diagnosis doc ! :thumbsup:

It hasn't gotten worse since I got the car (~4 1/2 months), I'm just wishing it won't after my warranty ends.

Any particular reason why this isn't consistent across gears ? Maybe (just guessing) because the deceleration is more abrupt in the lower gears ?

[repiv]

I see, thanks for the diagnosis doc ! :thumbsup:

It hasn't gotten worse since I got the car (~4 1/2 months), I'm just wishing it won't after my warranty ends.

Any particular reason why this isn't consistent across gears ? Maybe (just guessing) because the deceleration is more abrupt in the lower gears ?
Different gears, different ratios, different force that slams the spaces together. The low gears are the highest numerica gear ratios. You feel this the most because you are driving slower. Higher gears equate to lower numerical gear ratio and this can tend to cushion the abrupt slamming at the end of the space traversed. Also, the higher the speed, the more engine and road noise, the less you hear it even though it's still going on.
Unless you've done something really silly like horribly mis-shifted and ground gears and bent shift forks, you shouldn't be worried. If you have, well, that's between you and your tech.

[Boule]

Well I can't know what the previous owner did... I know I noticed the rattle the first week I had the car.

I did misshift once, for 5 to 2 instead of 4, but caught it before letting the clutch up completely, I don't think anything bad happened there...

Anyway, I'll keep an ear on it, in case it gets worse. Thanks for your help !