Unusual Noise at 40-50 mph

[jac04]

I have a 2021 Gladiator Mojave that I've had for about a month. So far, I'm really liking it, but...

It makes a noise that sounds like my HVAC fan motor is running at low speed, but I can only really hear it at about 40-50 mph. It is more of an 'electronic' sound like a motor running. My Jeep JK makes the same sounding noise when the blower fan is on low.

Now, it is not a bad sounding noise - in other words, it doesn't sound like something is failing. It is faint enough so that my wife doesn't notice it at all when sitting in the passenger seat.

It sounds like the noise is coming from behind the dash somewhere toward the passenger side.

The following DO NOT have any impact on the volume or frequency of the noise:
AC on/off
Fan speed
Recirc on/off
Radio on/off
Transmission gear
Engine RPM

Does anyone else notice this type of noise? Is there anything under the dash that might be the source?

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[Hootbro]

Spitballing here but does the sound change with the on/off of the re-circulation button?

I had a similar issue on another vehicle of what sounded like a certain speed motor hum and it turned out to be some leaf trash that got stuck on the fresh air side recirculate intake opening under the hood cowl . At certain speeds, the leaf clog would flutter like a vane at high pitch and made what seemed like a motor sound on the inside under the passenger dash.

 

[jac04]

No, recirc has no effect on it.

I may take a quick look to see if dropping the fan is easy. If so, I might take a look in there anyway.

 

[Knightindullarmor]

Ever driven big offroad tires before? Tire "hum" is noticeable, especially on vehicles without much noise dampening insulation (like Jeeps). 50+ mph is where it gets very prominent. Just one of many possible explanations for the noise you are hearing.

 

[869 KPH]

Not a Jeep - but I get a similar noise at about 55 MPH and have for years - I am somewhat certain it has to do with some dry-rotted foam gaskets where the hood meets the cowl. You could try to see if anything in that area looks loose, missing or just off to you.

Have some fun with it if you haven't already - pin point the speed it kicks in and just hover in and out of range while you come up with ideas.

And one final thought that I would do - remove the fuse controlling your HVAC to disable it entirely, and then go see if you can eliminate that from your list?

 

[jac04]

Ever driven big offroad tires before? Tire "hum" is noticeable, especially on vehicles without much noise dampening insulation (like Jeeps). 50+ mph is where it gets very prominent. Just one of many possible explanations for the noise you are hearing.

I've got a JK on KM2s, so I know tire noise. What I'm hearing is not tire noise. I've got the AT tires on the Mojave, and they are actually fairly quiet.

It is definitely an electronic sounding noise. It is a little higher pitched and sounds like the brushes on a slower turning electric motor. As I said, it sounds exactly like the blower motor on my JK, but it is really only noticeable at a certain speed range.

 

[TheGreatCO]

I have a Mojave and what you're describing doesn't sound familiar, but I'll give a listen next time I'm on the highway.

 

[jac04]

I have a Mojave and what you're describing doesn't sound familiar, but I'll give a listen next time I'm on the highway.

Thanks, I appreciate that. You definitely have to listen for it with the radio either turned down or off.

 

[jac04]

I was poking around a little on the JL forum. It sounds a little like the electronic throttle body noise detailed here:
https://4wheeldriveguide.com/jeep-w...l-fixes/#JLU_Jeep_Wrangler_High_Pitched_Noise

If that's the case, then it's just something that's the nature of the engine.

 

[jac04]

Well, I did a little more investigating of the noise. It is definitely not engine speed or wind related. Changing trans gear has zero impact. I taped up all the gaps around the hood, cowl & front windshield and no impact. It is 100% related to road speed.

With everything off (radio, fan, AC) and with the windows up, I can start to hear it at 45mph, it is loudest at 46mph, and it is gone by 47-48mph. It then comes back at a lower volume from 54-57mph. It is fairly subtle. My wife says she can't hear it no matter what, and I can't hear it with the radio on.

I actually think knightindullarmor might be right - the more I listen to it the more I think it is a tire noise resonance. My first thought was a front wheel unit bearing, but I don't think that would come & go like the noise I have.

Time to keep the radio on and try to forget about it.

 

[jac04]

I know I said I was going to forget about this, but against my better judgement, I've kept looking into this... It is more of a challenge to me now to try to figure it out.

I aired down my front tires to 28psi and the noise is still there - it sounds exactly the same and happens at exactly the same speeds. So, I think this rules out the tires (at least the front tires, and the noise sounds like it is coming from the front).

I also put the trans in N and shut off the engine, and the noise is exactly the same.

Changing between 2WD, 4H Auto and 4H has no impact on it. I have Selec-Trac.

Turning side to side doesn't appear to change the noise, although it is difficult to tell because of tire noise when turning side to side at 46 mph.

I dropped the glove box and used a piece of 3/4" rubber hose to listen the the area behind the dash, and the noise does not appear to be originating from inside the vehicle. However, when I put the windows down I can't hear any external noise over the wind noise.

So, I'm down to possible causes (things that are always the same based on road speed):
Front wheel bearing(s).
LH side front diff carrier bearing.
Something transmission or Selec-Trac related.
Rear drive shaft, wheel bearings, diff bearings (although noise sounds like it is coming from the front).
Some electrical component that would be active without the engine running and would change based on road speed (???)

I'll keep you posted if I ever find the source.

 

[869 KPH]

I know I said I was going to forget about this, but against my better judgement, I've kept looking into this... It is more of a challenge to me now to try to figure it out.

Good luck. Interested to see if you can figure it out.

 

[Hootbro]

Wish you luck also. Sounds like you are at the point where something has to get worse before you find it.

I know bearings can make noise at certain speeds and not others. Chasing noises can be a pain when you think it is one place but winds up being somewhere else.

 

[jac04]

Wish you luck also. Sounds like you are at the point where something has to get worse before you find it.

I know bearings can make noise at certain speeds and not others. Chasing noises can be a pain when you think it is one place but winds up being somewhere else.

Thanks. That's exactly where I'm at. Noises can be super tricky to pinpoint

I was actually thinking about changing the front wheel bearings because it is a fairly simple job, but then I had to stop myself for a reality check.

I told my wife I was going to bring it to the dealership to have them fix it and she said something along the lines of " you know they're going to laugh at you, and you don't want them working on your Jeep anyway...". I hate it when she's right.

 

[jac04]

For those of you playing along at home ...

I think I may have found the Some electrical component that would be active without the engine running and would change based on road speed (???) that I was wondering about.

The electric power steering pump. I believe that the pump motor speed is based on steering input angle and road speed. That would certainly explain why the noise sounds like an electric motor running, and it would also explain why the sound is not constant.

Now I just need to find a way to mount my gopro near the motor to see if I can record it making any noise. Or, like I've said before, I could just keep the radio on.

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