whup-whup sound from rear

[jocoman]

Need some opinions please.
I had just got off a major highway stopped and made a left onto a new highway.
As I gathered speed I could hear a whup whup sound seemingly coming from the rear. Not very load, but there. My wife described it as a helicopter sounding thing. When I slipped it out of gear the sound went away. Put it back in gear and give it gas and the sound re-appeared. Did not seem to make any difference if the highway veered to the right or to the left. Drove like this for maybe 15 minutes and decided I should pull over and inspect.
Nothing noticeable from a visual inspection. I crawled underneath and grabbed the axle and gave it a twist and a side to side motion. Not sure what it is supposed to feel like so I did the same on the other side.
I got back in and started running thru the gears and guess what... The noise is gone!
I'm planning a major trip in a couple of weeks and I am not sure what could be the issue.
Just so you know, I also have a lot of slop in my transmission linkage. I can get into every gear but sometimes when stopped I have a bit of trouble finding reverse. I have no idea if this is related.
So I am looking for opinions on where you think the noise came from and what I should do before my trip in 2 weeks.
Many thanks
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'86 Westfalia 2.0L Zetec
'97 Volvo 850 AWD Turbo
" The fun never stops"

[levi]

Since no one else has responded, I'll toss out some ideas.

Out of gear, so no load, I would guess eliminates something stuck to a tire or tire deformaties, that sort of thing.

One thing that comes to mind is a cv joint.

When they first start making noise it's often a faint noise at first after they've been thoroughly warmed up.

If it's been a while since you last greased them, the grease may have begun hardening.

When you were under the van pulling on the shafts you may have moved a little bit of grease into a needy joint, or, it may be that your 2nd ride was a short one, and the joint didn't get hot enough to start making noise.

Even if that isn't the cause, I'm an advocate of cleaning/regreasing the joints every few years.

You could test this if there's any long and very steep hills near you.
Go full gas and before you hit the top they should let you know.
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[jimf909]

To confirm ring a whup-whup sound from the rear of the van:
- in gear
- under load

Is this every gear? A single gear? Any rpms in particular.

Has it returned yet? It seems in addition to cv joints it might be a transmission sound.

I do sometimes get a wah-wah harmonic-like sound at a certain rpm and road speed (maybe 3500 rpm in 4th so 60ish mph). I’ve heard it for years and attribute it to some sort of harmonic resonance. Not sure if it’s the same as whup-whup.

Also, you may add something along the lines of “in gear” to your title so folks don’t just think it’s a ghost story.
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- Jim

[outcaststudios]

it does sound like a tire issue, or cv joint. the sidewalls can sometimes grow a bulge, from either the inside or outside of the sidewall so check both sides. if its not that the next place id look is the cv, then the rear brake drums...
_________________
'88Doka JX td
'69 westy
(rip)couple bugs
(rip)three type III"s
(rip) '81 vanagon
a bunch of french stuff,and 9 motorcycles.

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[E1]

Silly as it sounds, make sure your rear wheels are tight.

Seriously.
_________________
‘84 Westy, 2.1L with Digijet, 5.43 R+P, GT Gears
"Adding power makes you faster on the straights.
Subtracting weight makes you faster everywhere."
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[Abscate]

If you have not removed your CZvs and repacked them in the last 30,000 miles they are due. If the noise ended on moving the axle slightly, no damage has been done, they just need grease

Should be some write ups in FAQs. About 4 hours , first time . 2 hours or less for the skillz.
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.ssS!

[Volks Wagen]

Yes CV joint. Exact same with mine. Side to side wiggling spread a bit more of the 30 yr old grease and it shut up for a few 1000kms until I had to wiggle it again.

Don't worry about the gear stick. You'll find the gear eventually.
_________________
1973 1303 with AB-motor - sporadic
reconstruction as time permits, 1986 ex-Bundeswehr Doka - on the road again.

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