Cabin low frequency resonance - JeepForum.com
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post #1 of 18 Old 06-12-2021, 03:45 PM Thread Starter
shackleford
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Cabin low frequency resonance

I just bought a 2017 Summit V8 4x4. I noticed that when the AC is on, there's cyclical low frequency rumbling in the cabin. When the AC is off, I hear the same pattern but it's much less intense. It seems like the AC is amplifying the engine natural pattern.

Also, I hear a low frequency rumble when going over bumps. I drive in Auto mode with eco turned off.

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post #2 of 18 Old 06-12-2021, 06:03 PM Thread Starter
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The second issue is probably more important. I've read online that the noise went away for some people with replacement of the rear shocks. Should I also replace the rear struts and strut mounts? The vehicle has 61K miles. I literally just purchased a Mopar Added Care+ warranty for 5 years, 75K miles. I think that this would be covered if a dealer found issues there.
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post #3 of 18 Old 06-12-2021, 07:06 PM
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The rear suspension doesn't have struts, its a typical coil spring with a separate shock. But in your case it will have an air bag instead of metal spring. Replacing the shock mounts may help.

You may have bad motor mounts, or a bad belt tension pulley, however. Did what you read apply to the air suspension.

I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
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post #4 of 18 Old 06-12-2021, 09:18 PM Thread Starter
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Originally Posted by ColdCase View Post
The rear suspension doesn't have struts, its a typical coil spring with a separate shock. But in your case it will have an air bag instead of metal spring. Replacing the shock mounts may help.

You may have bad motor mounts, or a bad belt tension pulley, however. Did what you read apply to the air suspension.

Ah, yes. The Summit has four airbags, correct? I didn't think about the motor mounts. In what I read, people just mentioned the rear shocks. I may just have a dealership check these parts out.
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post #5 of 18 Old 06-12-2021, 09:41 PM
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The fronts are struts with air bags instead of steel springs.

I just got lost in thought. It was unfamiliar territory;
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac
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post #6 of 18 Old 06-13-2021, 06:01 AM
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How about tires? They all make noise dependent on where the tread level is at. The AC being on probably just changes the perception of the noise since it also makes a good amount of noise depending on what fan speed it is on.
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post #7 of 18 Old 06-13-2021, 11:37 AM Thread Starter
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How about tires? They all make noise dependent on where the tread level is at. The AC being on probably just changes the perception of the noise since it also makes a good amount of noise depending on what fan speed it is on.

Good point. I'll check the tread today. Yeah, the situation with the AC is fairly minor. I make take it to a dealership to have them check the few items that people have suggested above.
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post #8 of 18 Old 06-13-2021, 11:39 AM Thread Starter
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Originally Posted by ColdCase View Post
The fronts are struts with air bags instead of steel springs.

So, there are two front and two rear struts with air bags instead of steel springs? Are there also "standard" shocks?
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post #9 of 18 Old 06-13-2021, 12:13 PM
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Just a thought ... I occasionally get a very noticeable LF drone at very low speed over uneven pavement. I've had a vague notion that it might be related to some sort of feedback glitch in the active noise cancellation function. Come to think of it, I hadn't noticed it for a long time, and then it happened again last week, and this thread reminded me of it.

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post #10 of 18 Old 06-13-2021, 05:22 PM
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Summarizing what ColdCase mentioned which can get a little confusing, the front has struts with a self contained airbag. The rear has shock absorbers and a separate airbag.

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post #11 of 18 Old 06-13-2021, 06:05 PM Thread Starter
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Originally Posted by 19GCTrailhawk View Post
Summarizing what ColdCase mentioned which can get a little confusing, the front has struts with a self contained airbag. The rear has shock absorbers and a separate airbag.

Got it. Thanks for the clarification.
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post #12 of 18 Old 06-13-2021, 06:09 PM Thread Starter
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Originally Posted by BubbaATL View Post
Just a thought ... I occasionally get a very noticeable LF drone at very low speed over uneven pavement. I've had a vague notion that it might be related to some sort of feedback glitch in the active noise cancellation function. Come to think of it, I hadn't noticed it for a long time, and then it happened again last week, and this thread reminded me of it.

That possibility occurred to me as well. I wish there was a way to turn it off, but I think I'd have to just disconnect something.
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post #13 of 18 Old 06-14-2021, 08:57 AM
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Originally Posted by shackleford View Post
That possibility occurred to me as well. I wish there was a way to turn it off, but I think I'd have to just disconnect something.
Fuse pull would be the easiest. Not sure which one, look for the one for the amp. But that will kill everything sound related.

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post #14 of 18 Old 07-02-2021, 06:42 PM Thread Starter
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So I took it to the dealer to look at the rear suspension and something else. The technician said that he's heard this complaint before, usually from people who haven't had this vehicle/the airbags, and that it's normal and due to how the airbags operate.
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post #15 of 18 Old 07-02-2021, 07:22 PM Thread Starter
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I wonder if the Jeep has something similar to what's described in post #13.

https://www.clubarmada.com/threads/c...57/#post-99448

Quote:
But you may get the boom! Underneath in the back, in the rocker panels/fenders behind the tires you will find little grates. inside the grates are baffles made out of what feels like inner tube material. These vents are to release air pressure that causes the boom (cabin outflow vents). Like having the door open on a turbo prop on the ground with the engines running. If they get gooped up and can't flow enough air, then you get the pressure on the ears. If they flow freely and the back is not full of stuff, then you don't have to open the rear speed brake windows to relieve the pressure...
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