Intermittent "rumble strip" sound

[Tommy B]

Hello all,

Scratching my head on this one. 2003 LS v8, the car has of late occasionally produced a very brief shudder and sound, sort of like the sound when you drift onto rumble strips on the side of the road at speed. Only happens infrequently, but spontaneously and without apparent cause. Sometimes it's at highway speed traveling on a straight road, or turning at slow speed in a parking garage, or going over a slight bump in the road in a residential neighborhood. Doesn't last more than a fraction of a second. Can't predict when it will occur but something is clearly causing it. My first guess was ABS grabbing momentarily, but there's never a pull. I thought maybe a blown strut, but they appear OK, they bounce back just fine and aren't leaking so far as I can see. Now I'm thinking perhaps a suspension bushing or some other suspension part is failing, but that's just of course a guess. Anyone run into something like this? Thanks for any insight or suggestions on a potential cause.

 

[joegr]

Why are you guessing suspension for this? (BTW, you have coil over shocks, not structs) Is the car also shaking or steering differently or something else that you haven't said?
Why the guess about the ABS? Are you applying the brakes when this happens? (ABS will not trigger if the you are not pressing on the brake pedal. Traction control or AdvanceTrac can trigger with no brake input, but that usually also triggers a flashing light. In either case it wouldn't be nearly as loud as the rumble strip sound.) That said, triggering it with a bump does suggest it.

Does this happen when accelerating, when under power holding a steady speed, coasting, near a shift point, ..?
I've gotten rumble strip sound and feeling before due to torque converter shudder. This was not in an LS, but another car. It was resolved by changing the transmission fluid.

 

[Tommy B]

Joe,

Thanks for the reply. I can't associate it at this point with a particular action or event, it's really pretty random. I do different things to try to make it happen, but it doesn't cooperate. The one thing is, at times when it does occur, the car's going over a bump or turning at slow speed. But it has also happened on a completely flat, straight surface with no apparent bumps. The suspension guess is because the car's 16+ years old with 150K+ miles, and the various front end bushings are worn and probably need replaced. Not sure that would cause this issue but who knows. Had trans replaced at 115K miles, pretty early for a flush and fill, and the trans has been working flawlessly. I suppose I'll continue to try and drive the car to replicate the problem and try to pinpoint the conditions in which it occurs.

That traction control suggestion is interesting. This car has given me a lot of electronic problems, I've had to replace a couple of modules. The absence of a flashing light could be associated with module replacement or the basic electronic gremlins in these cars.

 

[FDR]

Does it sound like a different pitch/frequency between low and high speed? That'd be something to listen for. Are all of the splash shields and wheel well liners secured properly?

 

[04_Sport_LS]

ABS will not trigger if the you are not pressing on the brake pedal.

Not even with a faulty steering wheel angle, (yaw), sensor???

Just asking.....

EDIT: Ok... probably not ABS... but maybe Advancetrac?

 

[joegr]

Not even with a faulty steering wheel angle, (yaw), sensor???

Just asking.....

EDIT: Ok... probably not ABS... but maybe Advancetrac?

Yes, AdvanceTrac but technically not ABS. Of course, the results are nearly identical, but the causes are very different.

 

[04_Sport_LS]

Tommy,

Per chance... have you had an alignment done recently?

 

[04_Sport_LS]

My first guess was ABS grabbing momentarily, but there's never a pull.

This makes me think... that the car is thinking a wheel is locked up... so it actuates the ABS in an attempt to keep the wheel from locking up.

If you don't have a scanner... you might want to go to your local parts store and see if there are any stored codes.

 

[joegr]

This makes me think... that the car is thinking a wheel is locked up... so it actuates the ABS in an attempt to keep the wheel from locking up....

Again, this can only be true if his foot is on the brake at the time.

 

[04_Sport_LS]

So there's no possible way the car could be fooled into thinking a wheel was locked up, (faulty sensor or loose tone ring)?

Granted... a light should flash... but maybe its happening so fast the OP isn't seeing it.

I know on rare occasion my LS beeps at me... but when I look at the cluster there's nothing showing.

 

[joegr]

So there's no possible way the car could be fooled into thinking a wheel was locked up, (faulty sensor or loose tone ring)?...

So, assuming that a wheel stops turning ("locked up") or appears to have done so, without the brakes applied - how would applying and releasing (ABS) the brakes help? It can't release brakes that aren't even applied. That's kind of like turning the light off because it is too dark in the room.

I don't know of any ABS that activates when the brakes aren't applied. (Again, AdvanceTrac or traction control can.)

 

[04_Sport_LS]

Ok... point made. FWIW... I did find a Youtube video where a mechanic gives a good explanation. The magnet in the sensor gets weak... and the signal drops off at low MPH. But as you said... its while braking.

 

[joegr]

Yes, it can happen while braking. I did have some improper ABS activation on my Ranger, but it was because someone at a body shop bent a few of the tone ring "teeth" on the rotor (different setup than the LS).

 

[04_Sport_LS]

Tommy... here:

 

[FDR]

Just gonna point out my ABS/AT never sounds like a rumble strip anyway... ABS pulses are spaced too far apart and TC/AT doesn't pulse

 

[04_Sport_LS]

I can see where ABS pulsing could be compared to a rumble strip... or maybe a burrrrrrrp. Depending on the conditions... it could have a fast "chatter" to it.

How Anti-Lock Brakes Work

"Some ABS systems can cycle up to 15 times per second."

 

[joegr]

Just gonna point out my ABS/AT never sounds like a rumble strip anyway... ABS pulses are spaced too far apart and TC/AT doesn't pulse

Yeah, it's distinctly different to me too.

 

[Tommy B]

All,

Thanks for all the suggestions. Pulled the front wheels this weekend and found one problem, a rusted, detached sway bar link, photo attached. Not sure that would cause the noise but it is an obvious defect. Also put the code scanner on the car, none found. It's an OK scanner, Innova 3160, and scans for ABS as well. So I'll replace the broken link and cross my fingers.

 

[XR$Ti]

Late to the party... any update?

Not sure what the rumble strips are like in your area but where I am, they are pretty violent and much more awakening than an involuntary pulsing ABS. My experience has been (on another vehicle), the rumble strip sensation was a bad ball joint. Would seem to happen randomly but was really just turning the wheel slightly, like towards the crown on the highway for example.

If you haven't already, jack it up and do the 'ole 12-6 wheel shake.

I had a bad ABS ring on a different vehicle that would cause the ABS to come on by itself at low speed but the sensation was exactly like ABS pulsing ie non-violent and slowing.

 

[04_Sport_LS]

I had a bad ABS ring on a different vehicle that would cause the ABS to come on by itself

The older Ford Escapes were known for this. The tone ring would crack.

 

[Tommy B]

Late to the party... any update?

Not sure what the rumble strips are like in your area but where I am, they are pretty violent and much more awakening than an involuntary pulsing ABS. My experience has been (on another vehicle), the rumble strip sensation was a bad ball joint. Would seem to happen randomly but was really just turning the wheel slightly, like towards the crown on the highway for example.

If you haven't already, jack it up and do the 'ole 12-6 wheel shake.

I had a bad ABS ring on a different vehicle that would cause the ABS to come on by itself at low speed but the sensation was exactly like ABS pulsing ie non-violent and slowing.

Not yet, links supposed to be arriving today, will put them on tomorrow/Sun. Will post result. As stated before, crossing fingers!

 

[Tommy B]

Links came in, couldn't wait 'til tomorrow to find out. Installed both sides and test drove a few miles, no noise! Will take longer drive tomorrow, but hopefully that did it. Thanks to all for your input! Will update once I've driven the car for a few days.