That "helicopter" sound

[ganchan]

My Exp is a (2WD) 2000 with 197K on it. I've been getting a quiet "whump-whump" sound that gets faster with speed, resembling the choppy sound of helicopter blades up around 30-40 mph. It becomes unnoticeable at higher speeds, and doesn't seem affected by turning. It hasn't gotten any worse in the 8 months that I've owned the car. The previous owner apparently heard it too, but I think he just stopped investigating beyond the tires and cranked the radio up.

The other day I gave the car recommended maintenance to the tune of 2 new rear tires, alignment adjustment, and front wheel bearing repack. Haven't really driven it since then (ice storm), but am not counting on any of these changes solving the problem. If I discover that the sound is still there, what's the next thing to have the mechanic look at? All I can tell from my online research is that the issue could be rear wheel bearing, U-joints, pinion, hubs, loose wheel....

 

[stamp11127]

Get to a place where you are the only one on the road. Bring the vehicle up to speed, let off the gas and shift to neutral. Let the Expy slow down before shifting back into gear.
If the sound stayed while in neutral the problem is in the driveline. If it didn't, the problem is engine related.

 

[1955moose]

2 things you might check are the tires aren't cupped from an alignment problem, usually toe adjustment, along with worn shocks/struts. If you can carefully put your vehicle on four stands, and move around suv while assistant runs up to speed. Be extremely cautious doing this. Safety first always! Listen for any bearing rumble as well as driveshaft out of balance. The speeds your describing sound wheel/tire related, but who knows!

Sent from my N9131 using Tapatalk

 

[RonB1964]

One thing to keep in mind on the rear axle bearings is the axle serves as the inner race for the wheel bearing. The axle is held in with a c-clip and the bearing is a press fit in the axle housing. I've seen minor pitting on some axles I've changed out, which can cause some noise. Also, if the bearing is failing, you may see some gear oil seepage from the seal. If you have an excuse to change the rear diff fluids, checking the axle bearings may be worth a little extra time...

 

[ganchan]

Looks like the rear differential assembly is pretty much shot due to a slow oil leak/ooze that went unnoticed by the previous owner. (I only spotted the discoloration myself recently.) Fortunately, the auto shop is willing to install a used diff with a 6-month parts warranty from one of their trusted salvage yards. It'll have 119K on it, but anything I found myself (or any car I bought to replace this one) would be about that age anyway. They'll open it up and inspect it carefully to make sure it's in good shape before proceeding, so barring any unexpected weirdness it should be OK. Best I can do, anyhow.

 

[1955moose]

You'll be fine with a used diff. If it was coming out of a mustang, or camaro, I'd worry but a suv will be fine. If its a limited slip model, be sure to mention the Ford additive, but I'm sure they know that.

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[gtncpa]

That wump wump sound. Hmmm. Maybe it is the airflow in the truck. 5 years ago Ford Corporate called me to discuss this sound. On the call they called it a "Helicopter Sound". They had no solution on how to stop it but only asked the question if I have ever experienced it before.

If it is th eopen windows causing it, open the rear gill windows. That can help. I also find to get great air flow in the truck I open one back window. Play around with how far it is open on the highway to get the desired amount of air flow. The windows give the driver air differently. One side blows air on your face and the other side you feel the air come from behind you. It is also a great way to defog the front window.

 

[WoodrowUSMC]

My 2003 XLT has made the "Helicopter Sound" since it was new whenever the rear windows are down. Put the windows up and the sound goes away.