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Discussion Starter · #1 · (Edited)
My Ascent Limited is 4 months old and has logged 6000 miles. It has been trouble-free (except for below.)

When I drive on a smooth Interstate highway at a steady 70 MPH I sometimes hear (or sort of feel) a light clunk (or slap) at random intervals, approximately every 10 minutes. It seems to me that the clunk is coming from the rear of the car, but I cannot be sure. Nothing seems to induce this noise: I cannot relate the clunk to speed change, lane change, or anything else.

I do drive using the automatic speed control but it will clunk even when EyeSight does not see and has not seen any other car ahead for some time. I have not tried to test it with EyeSight disabled.

Has anyone else noticed this clunk, and what can be done to isolate the problem and then correct it?
 

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I had a clunk like that on a previous vehicle, after months looking for it I realized it was my fire extinguisher, freely rolling in the compartment behind the third row... Make sure there are no tools getting loose or something that fell, especially around the spare tire area. Also check that the spare tire is secured properly.
Just for a test, empty the whole car for a while. If you don't hear the clunk, problem solved.
 

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Then I'm not sure there's anything to do but have a mechanically-inclined friend ride in the third row and listen hard. Being closer to the sound should give some intuition as to where and what, or at least set up a better description to the dealership. Better yet, have someone drive and you listen in back (since you'll be describing to your service advisor).

But I'm with NotA. Nothng in the under-deck compartment? It's a smooth, wide plastic bin down in there, and wouldn't take much like a loose bolt rolling around.

F.S.
 

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I have no gear stored in the car.

So the clunk is coming from the drive train, not from inside the vehicle.
Do you have the hitch kit installed? If so, you may find that your drop hitch is clunking around. The dealership stores it in the tray under the floorboard directly inside the rear lift gate.

Mine started clunking after a few thousand miles, at which time I put it in a bag, and packed it in there in a way where it couldn't move.
 

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When the clunk comes from the drivetrain you should be able to link it to a specific movement or stress of the vehicle, or a bump on the road. The drivetrain has the rotational speed: but the clunk would repeat much more often. You have the movement of the suspension arms: you would be able to link the clunk to the bumps on the road. If something is lose on the axle you should be able to link it to turning left/right.
The fact it's so random and happens at 10 minute intervals makes it unlikely from the drivetrain. Could it be related to A/C? That is one system that goes on and off at intervals. Check if the hoses are secured properly, perhaps a hose under pressure moves a little and hits another plastic or something. Other than that, I'm out of ideas.

When you have eliminated the impossible, whatever remains, however improbable, must be the truth. – Sir Arthur Conan Doyle, stated by Sherlock Holmes.
 

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Are your tires inflated exactly evenly? Subarus don't have any 'give' in the AWD drivetrain, A repeating thud/clunk at highway speeds could be one of the differentials releasing.
Or not.
 
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