[designguy96]

I'm experiencing a thumping noise when I get off the gas and coast. I hear it mostly over 40mph. When I get back on the throttle the noise gets quiet or goes away completely. Sounds like "duh duh duh duh". Again, only when I'm off the throttle and coasting. Tires are couple weeks old, and I've had the shop recheck the balance. Shop drove it and couldn't find any obvious problem. It's a 2009 328xi wagon.

Any ideas of what I should look into?

[nsjames]

driveshafts is where I would start looking.

[designguy96]

Thanks. That was one thought I had. Just hard to check without removing, and I haven't seen any of the "brown dust" around the joints.

Would the driveshaft cause a vibration too? I mostly just hear the sound, no real obvious vibration with it.

[Phyrexia]

If your driveshaft center support bearing is bad, it could do this too. Might be difficult to tell from a simple visual inspection from underneath the car though.

[designguy96]

Car is all wheel drive, so I don't believe it has the drive shaft bearing. Drive shaft goes from transfer case to diff.

Differential fluids and transfer case fluid was changed this past year.

[Phyrexia]

You definitely have a CSB.

https://www.realoem.com/bmw/enUS/par...MW-328xi&mg=26

[desertman123]

The center support bearing is behind the heatshield for the exhaust

[designguy96]

Thanks. I was just considering the front since that's what I see most people replace.

Would a bad bearing come with a vibration? I really just hear the sound come and go, there isn't much of a vibration other than what the road creates.

[Volasko]

I'm confused why he would hear noise from the CSB when coasted vs. under load?

[designguy96]

Still trying to figure this out. Took it to the dealer, they changed a bad wheel bearing and that made the ride quieter but the thumping is still there. They claim that they switched wheels/tires with a car on the lot and that decreased the noise too, but they did not say it took it away.

Now around the same time this started I switched to non-run flat tires. Dealer test with run flats. I have a hard time believing it's the tires because overall the ride is smoother. Plus I hear the noise in the front, not in the back. If it where tires I would think you'd get a noise from front and back.

Anyone know of issues when they switched to non-runflats? I'm running Conti DWS 06

[nsjames]

do you have a bent wheel?

[Joebie]

Failing CV joints commonly make different noises under load or no load.

CV Joints usually sound like more of a 'rattle' than a 'thump' though.

Just thought I'd throw it out there, good luck!

Here's a video of what a failing CV join sounded like on my VW Golf

[longtermproject]

Double check your rubber on top of your windshield. I had a similar issue that was driving me up the wall with the thumping noise, turned out that a piece of the rubber had broken free and was flapping in the wind.