2013 Sentra: strange rattling/flapping sound when decelerating/braking

Maintenance/Repairs
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1

my wife complained about “strange sound” today…

2013 Nissan Sentra SR, 41K miles

sound comes from the front, and it is like some engine or transmission part is tapping against some body/undercarriage part: partially like rattling, partially like flapping and it looks to be in line with RPM, not with car speed

sound is NOT speed-dependent, I’ve also eliminated possibility of loose lug nuts, CV joints are smooth, front bearings show no signs of binding or looseness.

struts are in good shape, not leaking, stabilizer bar joints are in good shape, no loose parts found in suspension so far (spent 15 minutes under the car pushing/pulling every part imaginable)

problem appears only when car is decelerating, gets much noisier when gently braking

I’ve made an experiment with shifting “gear” (it’s CVT really) to “Low” to simulate engine braking and it made LOUD racket at that time. backing up to my driveway (which has substantial incline) did not make any “problematic sound”… not sure how one goes with another

the problem appeared suddenly, it was no warnings or lesser noise before

overall, car was maintained before to last long, but on such a low mileage it was not much yet to do

the only idea I have so far is a lower engine moint, which seem to be within 1/2 inch to the next metal part, but I can not apply enough force on it to make it “tap” the metal undercarriage part next to it

any ideas guys?!

2

Here is engine mounting diagram:

Screen Shot 2017-07-18 at 8.22.43 PM.png706×710 75.9 KB

I’m suspecting part number 6, but how to check if it is the root cause or not?

3

I had an VW RAbbit one time that would produce a similar symptom from time to time. It always turned out to be an exhaust hanger had broken, allowing some part of the exhaust system or the cat shield to rattle. Ask your shop to put it on a lift and check the integrity of the exhaust system hangers before presuming it is something else.

4

Thanks, George.
I’ve checked exhaust hangers and shields - no dice :frowning:

5

Each of these produces forces different from the other ones, you might experiment to see which sound each produces

  • Braking while coasting in neutral.
  • Accelerating in speed rapidly from a stop
  • Accelerating engine rpms rapidly (while stopped)
  • Decelerating engine rpms rapidly (while stopped)
6

Rattling appears here

No rattling from either of these tests

7

Can you have someone else observe while you are driving slowly and recreate the sound? It would help to at least narrow down the area it comes from. Front, back, right or left…

Perhaps another option is to raise each wheel, spin it by hand as fast as you can and have someone lightly apply the brakes. There are just too many possibilities that can cause this without more details.

8

by opening windows and listening from inside, this sound definitely comes from the front, from underneath, no specific location of left/right

I was spinning wheels raised off the ground already, as well as trying to “push” through the wheels to nudge engine/transmission - not a squick :frowning:

good point on trying to apply brakes - will do it shortly

9

This is the stumper (not using brakes here, right?).

10

YES

…answer has to be > 10 chars :slight_smile:

11

This test could not reproduce any “problem sound”: everything was smooth while rotating both wheels one direction, then another direction and lightly applying brakes

12

Re: Rattling occurs when braking when coasting in neutral

Given the others I mentioned above produced no rattling, unlikely to be engine or transmission mounts. That pretty much leaves the suspension or exhaust components. When you brake in neutral, the front end of the car’s chassis moves down, and the back end moves up. That motion affects both the suspension and exhaust system. So likely the problem is something loose among suspension bushings, ball joints, springs/struts/shocks, exhaust hangers, exhaust shields. Usually what a shop would do is put the vehicle on a lift and start poking around, mildly levering suspension components, looking for any unusual amount of play. There has to be play somewhere for rattling to occur. Some shops have a gadget called “chassis ears”, multiple microphones than can place at various places and listen when driving the car. That might be worth a shot if you get desperate. Usually just the normal shop inspection above figures it out eventually.

Problems in the brakes themselves of course could cause this. Like missing anti-rattle shims.

13

Can you feel feedback in the brake pedal or steering wheel when this happens? Does the pitch of the noise change as you slow down? Is it a metal on metal rattling?

14

For now I’ve ordered that bottom engine torsion linkage, as it is has some strange play into it and it is easy to replace. $25 waste if it does not solve the issue.

suspension seem to be rock-solid, same as exhaust… these were the first ones I’ve explored

15

no feedback neither on pedal, nor on steering wheel, sounds is not linked to the vehicle speed, but ppears only close to idle RPMs, any revving up eliminates it

16

Does your vehicle sport a stabilizer bar/link in the front suspension? From what I’m seeing here it does. If so, all the bushings, clamps, associated w/that should be a suspect. Stabilizing linkages are a common source of noises, especially worn bushings.

17

it has a roll-bar (as any car nowadays?) and that thing is OK on links and on bushings

it is no cross-bar under the hood - Sentra SR is not as sporty as it used to be few years back, where it used to have Altima’s 2.5 enigne and really sporty suspension :frowning:

18

[quote=“GeorgeSanJose, post:12, topic:106016”]
Like missing anti-rattle shims.
[/quote]I was not aware of brake anti rattle shims until my Wife’s 2002 Subaru Outback exhibited sever front end shaking when brakes were lightly applied on a several mile 6% downhill mountain pass. I was driving. Once we got to the flatlands it was normal. We called the dealer and they said bring it in for a shim replacement recall. Shim replacement solved the problem.

1 Like
19

That’s a lead, I will research, thanks!

20

I’ve checked dealer repair manual and front end has no shims, it is apparently quite primitive McPherson front suspension mounted on floating under-frame: