"harmonics" noise

[factsmanmp]

A few years back, found a beauty...2005 Jamboree GT, 30 ft with only 2000 miles on it. Bought it from original owner and when driving home on freeway, thought someone was honking at me! Soon discovered it was coming from the motor home. Called the seller when I got home and he said it was coming from one of the shrouds or antennas on the roof. Informed him I was having my mechanic take a look. Checked wheel bearings, rear end, drive shaft, U joints, transmission and no one can figure out what the noise is. Happens between 50-65 mph, not as bad under load or coasting but definitely throttle related. Checked heat shields, installed Banks system, still the same noise. Any ideas???

[SailingOn]

My Winnebago View made a similarly speed-related hum which disappeared entirely when I removed the hub caps ("wheel simulators") and left them in the garage.

[T18skyguy]

This is just a guess, but I'm thinking the drive line pinion angles are wrong. The reason I think this is the problem was present when the rig was new. You can replace the carrier bearings, but if the angles are not adjusted correctly the problem will still be present. Use a digital angle gauge, and using the lip of the transmission pan as a baseline, take a reading and write that down. Then take a digital reading in the middle of the first driveshaft. That reading should be 1.15 degrees lower than the trans pan edge. The second driveshaft should be 3 degrees, and the fourth 4 degrees. This is on my rig, but your rig may vary. The way to adjust the angles is by putting 1/4 inch plates under the yokes which lower or raise it depending on your needs. If the yoke at the differential needs raised that is done with a shim under the springs. Drive angles must be more than 1/2 degree and less than 3 degrees from each other. People who can provide this hardware are L&W Engineering at 574-825-5351. A two driveshaft setup would be different but the same principles apply. It would be good to consult a professional drive line shop. Camping World and regular mechanics will not solve that kind of problem. A simple and easy way to rule out this problem is to jack the back end up, put it on strong jackstands(on concrete), and run it up to 55-60 mph and have someone observe the driveline for vibration.

[Rick_Jay]

factsmanmp,

You said that the previous owner suggested it was a shroud or antenna on the roof. Have you investigated those options?

~Rick

[factsmanmp]

well, completely forgot about this post and almost 3 years later, still having the same noise. 42,000 miles now. Changed out tires with no effect. Not sure why a IAC valve might be the cause since it only happens a driving speed of 55-65 mph. And the noise is still there after camping and using the sinks. Drive line and u-joints were checked but may go ahead and replace the center drive line carrier bearing.
Thanks to all for your thoughts.

[klutchdust]

My 2009 Itasca Cambria had a hum related to throttle pressure similar to the sound of a bad wheel bearing or rear end bearing. i changed the gear lube in the rear end to synthetic and it went away.. Unit had 19K on odometer and was doing this.

BIL has a Monaco class A with a wind detector to close awning automatically. it was spinning one evening and was making a howling noise, he said it sounded like motorcycles driving by.

[YC_1]

I would take a look at any antennas on the roof that may have an open coil design. That is, a spiral section. I have wrapped them with heat shrink tubing on ocassion to stop the nusiance

The previous owner suggested this. Maybe he noticed it after installing it. could be a cellular, cb, ham etc antenna.

[ernie1]

I had that same problem and at the same speeds. Went away at a higher or lower speed. Sounded like someone blowing across the mouth of an empty soda bottle. Chased the noise for a couple years and finally traced it to the drain for the galley sink! What happens is that if the trap for the sink is empty, the air blowing across the vent on the roof will cause the noise and give you the soda bottle noise. I now always tighten the stopper on the galley sink and if I forget and the noise starts up, I run some water down the drain and then insert and tighten the stopper.

[navegator]

As stated above center carrier bearing, a U joint or the drive shaft if it is two units that they are slightly misaligned, it only takes one tooth on the splines for it to wobble, vibration will be not be to noticeable, road bumps and suspension bounce will mask the vibration, and the center support will also dampen the movement but not the noise.

navegator

[j-d]

Is it a hooting sound like a saxophone or ship's whistle?

You haven't said which chassis you have, but the Idle Air Compensation (IAC) Valve is a common failure and makes the sound I described.


Installs with two little bolts and one electrical connector, costs around $40

[carringb]

What happens if you put in neutral when you coast?

I'd be suspicious of the center driveline-carrier bearing.

[DrewE]

Tire tread pattern, maybe?