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**CountryFit** · 11-01-2019, 11:05 PM

Just about to wrap up this year's travel after over 10k miles, two days ago in San Antonio I noticed a loud humming (almost roaring) sound from rear end while picking up the speed, i.e. on rump to get on highway. The sound is unnoticeable on flat road at steady speed.

I have tried the followings -
1) Engine has no error signs on dash; oil was about 1 gallon lower. Added oil.
2) Transmission fluid level is right on the mark.
3) Re-lubed the sliding drive shaft.
But non of above worked.

I am not sure if a bearing somewhere is worn, and no idea what else to look at. Any pointers/suggestions are welcome. TIA.

On edit: Basic info:
- Coach: 2000 Intrigue
- Engine: ISC 350, maintenance done annually
- Transmission: Allison MD3066, changed to TES295 compatible fluid 5 years ago
- Mileage: 98000
- Chassis lubed annually

IASM · 11-01-2019, 11:42 PM

could it be your fan running at high?

guardrail53 · 11-01-2019, 11:56 PM

Steven, I would first check the U-Joints, and while you are under there, check the level of your rear end lube! Take out the plug about halfway up and if no 90W oil comes out, stick your finger in and see how low it is! If it is full, and runs out when you remove the plug, (good) put the plug back in and go to the next thing! Take a big screw driver, or pry bar and put it in the U-Joints and make sure they are tight, with no slop! Also grab the drive shaft, and try to move it up and down, at the front and rear, to check the input bearings in the rear-end, and the output bearings in the rear of the transmission!
Also, do you have a infrared temp gun? After a run, take it and shoot everything under the MH in the driveshaft/rear end area, and see if you get any hotspots!
Look at the inside of your rear wheels, for lube leaking out, and if they are wet/oily, or you see stains on your wheels/tires, you have a seal leaking, and most likely a wheel bearing bad! Any heavy truck shop can check it out for you, and most TA's/Petro's can and will fix it for you! Good luck, don't ignore it, and get it fixed quickly, so the cost is kept at a minimal amount! Rail!

cntrylife · 11-02-2019, 12:02 AM

Turbo whine?

Kodiakan · 11-02-2019, 01:55 AM

Quote:

Originally Posted by cntrylife

Turbo whine?

That would be the next thing I would check.

twinboat · 11-02-2019, 04:01 AM

Check all of the short connection hoses along the intake air, charge air cooler, 3" tubes. They run from the turbo to the cooler next to the radatior and back.

A split one will open up and leak boost pressure causing that kind of sound.

You could have someone hold the foot brake on and step on the throttle, slightly, to create some boost ( very little at idle ) and watch/listen for the sound.

Bobby F · 11-02-2019, 04:05 AM

All good suggestions, but do the rear-end lube check before you put another mile on.

**CountryFit** · 11-02-2019, 07:19 AM

Big thanks to you all! Really appreciate the fast responses!

IASM: In the past when I climbed steep hills, the fan was on high but there wasn't such a sound. But I'll check it, make sure it was not the cause.

guardrail53: All good points! I'll add those to the maintenance checklist and pay attention to those places. I have the big allen wrench to open up the differential port, and will check it along with other items you mentioned early this morning.

cntrylife and Kodiakan: Yep, turbo is one of my focuses.

twinboat: as always, great pointer on the issue. I'll look into the hoses, and possibly flip up the bed and check that area from top. (BTW, thanks for the camping site suggestions in New York! We stayed at Cathedral Pines Suffolk County Park near mid island for 4 nights and Floyd Bennet Field for 3 nights. Both were perfect place to stay, couldn't be happier

).

Bobby F.: Yep, need to get it nailed before hit the road again.

TR4 · 11-02-2019, 09:49 AM

Exhaust drone?

Bill

**CountryFit** · 11-02-2019, 11:00 AM

Quote:

Originally Posted by TR4

Exhaust drone?

Bill

I wish it were. The noise starts as soon as I press the pedal to take off. Thanks!

camper8251 · 11-02-2019, 04:44 PM

My old lady does it if I dont feed and water her.

gnvrvin · 11-02-2019, 05:56 PM

Steve,

What kind of hum noise is it. When I think hum I go to an electrical 60hz sound. Which I know its not.
We once picked up a high pitch whistle which was an exhaust leak
Keep us posted, always good to educate everyone else as well

Good Luck,
Greg

Smitty77 · 11-02-2019, 06:10 PM

Quote:

Originally Posted by CountryFit

I wish it were. The noise starts as soon as I press the pedal to take off. Thanks!

Do you get the sound when in neutral and raising the RPM's. If so, it's engine related, not wheel train related. If not, then it's wheel train related... (At least in my simple view of the world. Which being married, I've been informed a few millions time - is often wrong

!)...

Best, and looking forward to you closing the loop back,
Smitty

**CountryFit** · 11-02-2019, 07:09 PM

Greg: It's a loud low frequency humming sound + roaring sound, more like working very hard but not moving.

Smitty: When parking brake is on, pressing fuel pedal does not increase the level of the noise. However, after thorough check from under and above, I did find something I think it might be the cause. I'll try to describe it in more detail in next post.