My 2004 makes a very loud Hmmm sound in low gear under load, 65 mph, 2500 rpm?

Hi Folks,

Just wondering if anyone else has experience with this noise i am hearing. I have a 2004 158" bus, and find that around 65 mph, in low gear, around 2500 rpm, if I am under load, say climbing a small grade, or have weight in the vehicle, I hear a fairly loud Hummm noise coming from underneath, when I press the gas pedal not to the floor or anything, just pressing the pedal an inch or so.

It is a very low frequency noise, almost like a subwoofer kind of noise?

I am under warranty, so I just want to make sure i can "help" a tech with diagnosing this as I hate going back for the same problem on numerous occasions?


Any insight to this would be very much appreciated. I have read about a valve in the fuel rail or something here, common failure on 2004's, but was not sure if this is what this sounds like?

Many thanks in advance,

Tibor

to bad you could not record it..

some many things it could be from a belt
to a fan clutch.
list goes on.

Tibor... how many miles? 2500 or 3500? The more info provided on these types of posts, the better we can guess at the cause

Maybe a noise from the rear axle, a bearing perhaps?

if it is a rear bearing or axle you should be able to change the pitch
of the noise by turning the wheel a little when it make the noise.

It is a 2500 with 18K miles.

It seems like it may be this pressure relief valve on the fuel rail, or the fuel lines themselves rattling in their clamps on the frame. These are the theories I have read.

This occurs with no load in it, just when there is load on the motor, meaning I press the gas pedal about an inch, and that load of the weight of the vehicle itself is enough to cause this deep trombone type sound, at low gear, with a little gas only, and turbo hardly whining......

Sorry man, trombone noise is a new one on me.

I've heard of A/C systems making such noises but that's it.

Maybe one of the other members have heard of this?

same problem with my 2004 2500 bus.

its the differential... you sure 2500 rpm? it should happen just under that rpm.

Is this hum noise is more obvious when there is load or going uphill?

dealer told me when i was buying mine they bought back one
that had a rear end prob that they never could fix even
after changing the rear end 3 times..i guess noise went
away for few thousand miles then came back

Yes,

it is more obvious with a load or going uphill. It could be less then 2500 rpm too, say 2300?

Then its a exact problem on every bus or cargo with our differential.

My dealer is worse, they can't hear anything

My licensed master mechanic told me it is caused by under rev (not enuf power) to spin the rear axle. Its not good to the transmission in long run hearing that noise since the whole 8500 lb is now driven (pulling temporary) by the tranny.

I don't hear anything on the cargo version with different spec differential though. But drove like a real tractor we service everyday.

When you say spec on "our" differential (I have a 2004 158 bus), are you talking gear ratio, or some other common denominator?

Is that your silver cabrio in the picture?

I think this is the same one mine makes at a lower 1700 rpm, part throttle, almost a howling noise. Two mechanics told me it sounded like an exhaust harmonic or maybe a loose baffle. One crawled underneath and pushed and pulled on the exaust and was able to make a similar sound. It seems to be coming from the centre exhaust hanger which is kinda light duty. We think it might be vibrating under the right load causing the sound.

I'll update when I attempt to fix if it works.

Derek

Thanks Frostback,


I am anxious to see what you come up with, is yours also a 2004?

Mines an 03 140 passenger. It doesn't fit in my Garage so I got to wait for some decent weather before I attempt to fix.

I have the same noise at 50K miles, under a load by just pressing lightly on the accelerator. I thought it might be the limited slip differential ... slipping a bit. It sounds like a low rumble.

Some folks have called this noise an intake HOWL!!!!

Still a mystery, but all that have it seem to state it ocurs right around 70 mph, and it more noticabvle when there is more load.

It is annoying and load I have to say!!!


Tibor

It isn't a howl. it is a physical vibration. something is slipping, or going out of harmonic balance, or otherwise not working smoothly when this noise occurs. Until I smell smoke or see shiny metal parts bouncing on the road in my rear view mirror, I guess it isn't a big concern.

My '04 158 2005 makes the same kinda noise, more pronounced when slowing down, I've read other posts on the site seems like it happens a lot. I wonder if that's what they call RSN.....

I bought my cargo van used from Autowest dodge in Fremont(not an authorized sprinter dealer) w/ 82k miles about a year ago, 152k now thanks to Ukiah delivery route, done pretty good with maintenance e.g oil change filter etc. had a tranny oil and filter change @ 130k but sound seems to get worst though:bash.

My 2004HC MWB Wagon (140", passenger) does this at 1250 and at 2500 under light load, but increasing throttle if in top gear only... that is, at about 30-35 MPH (not common to be in 5th at this speed) and at about 65 or so... (no, this is not precise, it is memory of 45 y/o male with wife and 2.5 kids in highschool at same time, one soon to be in college)...

I believe that the lockup has happened, the torque is building, the resonance of everything is converging, and the whole drive train begins to transfer its resonant frequency through a point which sends it into the cabin... I also am pretty sure that it can affect fuel economy due to the power loss to vibration/resonant behavior!

I still only get 20-21 MPG at best. After 26K Miles I still don't get close to the reported 25+ MPG.

Also, since my exhaust was stolen and had to be replaced, this frequency and intensity has changed and can be heard at about 65-70 MPH as a frequency specific "drone" that seems to come from a spot behind/below the driver (as the driver hears it)...

Those of you that get higher mileage, do you get this resonance?

If you get resonance, do you get good MPG, anyone?

Thanks,
KenB

Has anyone else had these symptoms recently. I now have 55K miles and it seems like it is getting worse. I have read more of these problems in the 2007 or newer versions than the T1N in this forum.

If I still have powertrain warranty remaining, would this be covered? Where should I take it to have a look? MB or Dodge?


Thanks for any updates on this annoying sound that makes it rather loud in the cockpit on the highway under load....


Cheers,


Tibor