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Discussion Starter · #1 ·
I'm seeking help with diagnosing what is causing noise and vibration with my S40 AWD. I noticed this noise that I'm 98% sure is coming from the rear maybe two months ago and it's slowly getting worse. Whatever is making the noise is also causing a vibration that can be felt emitting through the floor of the car. I'm assuming the vibration is caused by the noise source, though there is a slight change it could be an out of balance wheel, but nevertheless it goes in sync with the noise.

Before I go any further, here's a gopro video from under the car so you can hear the noise: https://www.youtube.com/watch?v=OgbySedz0o0&t=0s

The noise kind of makes you think of something out of balance rotating and wobbling around under the car. My first thought when I noticed the noise was the propshaft (the center support bearings rubbers feel very loose and tired), but from the footage I determined propshaft is rotating over two times the speed of the tyres and the noise goes with the tyre speed, so that kind of rules the propshaft out in my mind. What comes to mind next, are the rear drive axles, but the sound doesn't really seem to change much with load/no load - granted it is probably a bit harder to tell with the rear axles + increased overall noise during acceleration. Next, could it be a rear wheel bearing? But the sound doesn't change when I do zig zags trying to shift the load from side to side - maybe still possible? But I think a wheel bearing noise would be more constant "angry engine" type noise instead of "hum, hum, hum" or "wa, wa, wa". Then I saw a youtube video that described similar problem ending up being a stuck brake caliper. However, in my case the sound doesn't change at all with braking and none of the rotors feel excessively hot after driving.

At this point I thought I'd post this here in hopes someone has experienced similar symptoms and found the culprit. Meanwhile I continue to investigate the source with new methods... I would like to avoid just randomly throwing parts at this. Thank you for your time.
 

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How many miles on it?

Really hard to see the propshaft rotation in the video due to the low light, however it does appear to be oscillating out of round. The CV joints will wear and bind. You really have to remove the propshaft and visually inspect the joints. Obvious signs would be torn boots (typically the forward one, since exhaust heat tends to cook that end). If you have anywhere close to 100K miles I would consider them suspect.



hard to see in this pic, however the grease is cooked. Upon disassembly, wear grooves were evident in the hub, and the ball bearings have score marks (no pic). Be very careful to mark the three main parts (hub, cage, outer housing)- they need to go back EXACTLY as removed relative to one another.



Rear wheel bearings also. To check them you may have to remove the rear calipers in order to manually feel play in the bearing, as the brakes in place will inhibit axial play.
 

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The louder noise reminds me of the physical feel of the bearings go bad on the front. I replaced them and now have the hu hu hu you hear in the same pattern (speed of the tires) and I only have 1 rotating assembly left to change - my duralast axle out for my oem rebuilt one. Sounds like you got a rear axle going bad IMO. Bearings are cheaper! Me personally I'd find some junkyard units and have them shipped to me, rebuilt, and reassembled on the car with some new bearings.

If you think it's the propshaft, get under there with an allen key and remove it and go for a drive. Easily doable and provable - just be sure to mark it's original position for reinstallation.
 

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Discussion Starter · #4 ·
Thank you for your insight so far. The car has ~90k miles on it.

Yeah, I noticed the propshaft is not rotating completely centered and is most likely in need of some maintenance. However, I don't think it is the source of the loudest noise I want to get rid of right now (it starts to get unbearable loud at higher speeds).

I jacked the rear of the car up and rotated the rear wheels by hand. The right side wheel made much rougher sound than the left, which makes me suspect a wheel bearing after all. Since they are not the most expensive things in the world, I ordered one - fingers crossed...
 

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2007 Volvo V50 T5 AWD M66
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I've done both rear bearings and front right, not sure why my front left hasnt gone bad yet.
When both my rear bearings went the whole car shook and and vibrated along with a horrible drone noise that was louder than the radio at full volume.
 

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Discussion Starter · #6 ·
I've done both rear bearings and front right, not sure why my front left hasnt gone bad yet.
When both my rear bearings went the whole car shook and and vibrated along with a horrible drone noise that was louder than the radio at full volume.
Sounds interesting. I hope it's just the bearing for me too, but let's see once I get it.

As a side note, it's crazy how much the rear diff/haldex box twists around under acceleration. It seems be sending a good bit of power even at part throttle which is s bit unexpected...
 

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Discussion Starter · #7 ·
Update:
I received my rear wheel bearing/hub. With a bit of work got the old unit out and it is definitely shot.
However... Curses, curses, curses, the new bearing I got does not fit this car (apparently, I ordered it a bit too much in a hurry). It has threads instead of through holes for the 4x fastening bolts. I considered drilling them out and adding an access hole, however the "frame side round lip" diameter is 2 mm smaller than the correct one. So, I ordered a new bearing assembly again, but this time it should definitely be the correct part... I will update hopefully in a week if it cured the issue.
If anyone is curious, the wrong one I got is this damn thing: https://www.vsm.skf.com/uk/en/products/VKBA6791
 

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Discussion Starter · #8 ·
Finally got the rear wheel bearing/hub assy changed with the right part. It cured the vibration and noise. It was relatively easy job and now the car drives smooth. :partywave:
 
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