Painful low frequency drone/pressure in cabin (16 Viewers)

[LJE]

Alright, have another odd one for the forum...

I just got Lazarus (2005 LX) back from the alignment shop - so it's the first time I've actually really been able to drive it ever! Super excited about that. Mechanically drives like a dream & all is well on that front.

However, above about 40 miles per hour I get a super low frequency 'drone' in the cabin. You can barely hear it, but holy crap does it make my ears hurt - feels like it's building pressure on my eardrums. If I'm going down a decent hill (i.e, no load on the engine) it goes away even at speed. I can rev the engine at a stop and it doesn't do it - seems like it has to be under load.

I do have Doug Thorley headers on it, but I've near heard of anyone having this issue with them.

Opening the rear quarter windows helps a little, but not much.

Has anyone had an exhaust leak somewhere cause something like this? That's my best guess - some sort of odd leak that's causing low freq pressure spikes. Open to other ideas though - it's a weird problem!

 

[MongooseGA]

First thing to check-

Do you have your frame weight in place?

 

[LJE]

First thing to check-

Do you have your frame weight in place?

You know, that's a good point. I just checked & it's absent from my truck. I'm under the impression that the weight was mostly for vibration damping at idle though?

Other thing I guess it could be (just brain storming) is the tires being out of balance/round (unknown history, and probably sat for at least a year). I wouldn't think that letting off the accelerator at speed would matter though in that case, but I might see about getting those tires balanced.

 

[Bisho]

OK, probably silly, but are all your windows closed? I know if my daughter opens the back window I get the thumping at speed, unless I open another window.

 

[LJE]

OK, probably silly, but are all your windows closed? I know if my daughter opens the back window I get the thumping at speed, unless I open another window.

They are all closed, but the pressure is not dissimilar to the cavitation you get with a single window open...

 

[LXJake93]

Frame Weight - Worth Keeping?

Hello, I just removed the frame weight from my 2002 LX. It was just flopping around, the bushings are completely shot. It was located below the passenger door. Does it do anything? Is it worth keeping? I would need to find some kind of rebuild kit. Based on my research this part is...

forum.ih8mud.com

It could just be your tires or wheel bearings or whatever.

 

[MongooseGA]

I just caught your comment about letting off throttle and feeling it.

Check your u- joints.

 

[LJE]

I just caught your comment about letting off throttle and feeling it.

Check your u- joints.

After a bunch more test drives, I have to correct myself. The noise stays the same at any given speed, whether I'm applying throttle or not. Downshifting (increasing RPM to maintain speed) doesn't change the noise either.

After thinking about it all day, and having the wife test drive it, we're both a little stumped.

There's no vibrations that corrospond to the noise/pressure - it truly is just something you feel in your ears.

I checked U-joints (felt good) and even pulled the rear driveshaft (no change).

Tires are a unknown - I know this vehicle sat for a while before I bought it, but the tires are only 4 years old (manufacture date) with lots of tread left. Had the balanced checked on them today, no change to the noise. As mentioned, no vibration or anything. I may try to find somewhere that can road force balance them though just in case.

Wife says it gets much better when you roll down the middle row windows (it's a bigger difference than rolling down the front windows or opening the rear quarter windoes). I also noticed that if you roll just one window down, you don't get the cavitation/'whomp whomp whomp" noise that you usually would with just one window down when driving at speed.

I'm leaning towards I've got something that's letting air in/out that shouldn't be, and our ears are picking that rapidly changing pressure up. A Spectrum Analyzer app on my phone says it's right around 40hz - playing a YouTube clip of that tone, I'd agree with that.

I'm not quite sure yet what to do with all that info, so it seems like I've got some thinking to do...

It's a shame, because this is my first time driving an 100 series, and I love it - just need to get it to stop assaulting people's eardrums...

 

[Dirt Ferguson]

I wonder if there's something that crawled into the vents and made a nest? any weird smells? does the drone change when you ramp up heat or ac?

 

[LJE]

I wonder if there's something that crawled into the vents and made a nest? any weird smells? does the drone change when you ramp up heat or ac?

It's lived in my garage since I bought it (March) and have been doing all the work to it, but I guess I can't be sure about prior to that. No weird smells from the HVAC, and no change in pressure/symptoms from changing settings best I can tell. I'll revisit that at some point to confirm though.

 

[LXJake93]

Dumb question… are all your floor pans solid? Super strange question, but yah never know!

 

[Dirt Ferguson]

a video recording of the sounds would help, if possible.

Is there a place in the cabin where you can hear it more or less? Near the floor? Near the front or rear of the vehicle?

 

[MongooseGA]

What happens if you stick the transmission in neutral while you're going down the road and experience the noise?

 

[LJE]

Dumb question… are all your floor pans solid? Super strange question, but yah never know!

We are well into the "let's look into all the crazy theories" zone, hahaha. All the floor pans are solid though - I have pulled the carpet when I first got the vehicle to clean it. Also, rust free CA vehicle.

a video recording of the sounds would help, if possible.

Is there a place in the cabin where you can hear it more or less? Near the floor? Near the front or rear of the vehicle?

I'll try to grab one of those in the next couple days. I haven't had a chance to have a second person actively in the car with me, so haven't been able to move around to see if it gets better/worse.

What happens if you stick the transmission in neutral while you're going down the road and experience the noise?

No change to the noise/pressure when I kick it into neutral.

 

[2000UZJ]

I had a nasty gear wine in my ‘06, changed every drop of fluid in and resolved itself. What’s your transfer case, gear and trans fluid status?

FYI - my transfer case fluid was low and extremely dirty. I flushed it twice and I’ll run it for a few thousand.

 

[LJE]

I had a nasty gear wine in my ‘06, changed every drop of fluid in and resolved itself. What’s your transfer case, gear and trans fluid status?

All brand new actually - 75w-90 Mobil synthetic in front/rear diff & transfer case. Brand new Valvoline max life in the transmission (full 12 quart fluid 'exchange'). Level was set as per the FSM.

 

[2000UZJ]

All brand new actually - 75w-90 Mobil synthetic in front/rear diff & transfer case. Brand new Valvoline max life in the transmission (full 12 quart fluid 'exchange'). Level was set as per the FSM.

I guess the long way to check is pull front drive shaft and flanges and see if it’s coming from the front differential. Carrier bearings do go bad, but seem super rare on these platforms.

That’s the only way to stop the diff from spinning without removing CV’s and that sucks.

 

[LJE]

I guess the long way to check is pull front drive shaft and flanges and see if it’s coming from the front differential. Carrier bearings do go bad, but seem super rare on these platforms.

I'm not totally against that, however, I feel like if it were a mechanical issue I would be *feeling* it too.

40hz is a pretty low frequency, so if something in the truck was shaking at that frequency loud enough that it causes physical ear pain I would expect it to travel & and I'd be able to feel it everywhere. That's what is leading me to think it has to do with air pressure fluctuating.

However, I'll add pulling the front driveshafts to the list though!

 

[2000UZJ]

I'm not totally against that, however, I feel like if it were a mechanical issue I would be *feeling* it too.

40hz is a pretty low frequency, so if something in the truck was shaking at that frequency loud enough that it causes physical ear pain I would expect it to travel & and I'd be able to feel it everywhere. That's what is leading me to think it has to do with air pressure fluctuating.

However, I'll add pulling the front driveshafts to the list though!

Low frequency vibrations could be absorbed my body mounts, but the sound transfers.

Another thought is pull your radio fuse and see if something is interfering with the H/U?

I’m totally spitballing. I can make my speakers buzz by setting my JBL amp to the wrong speaker OHM.

 

[jaewastooshort]

Electrical interference sounds like a plausible rabbit to chase... I've had weird ground issues in another vehicle that led to a buzz through the speakers that corresponded with engine RPM...

I had a seemingly similar issue with air pressure when we were driving through Colorado/New Mexico last month when there were some high crosswinds. It felt like the outside air pressure was creating a vacuum and pulling the driver's side door away from the body enough that it broke the seal on the door weatherstrip (about to replace it on both front doors), and every time it would lose that seal we'd get a weird drone that reverberated in the cabin like when you have a window cracked or open just wrong.

If the drone is more or less constant, it sounds less likely that this is your exact issue, but the weatherstrip rubber on the doors might be something to at least inspect.