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Discussion Starter #1
Hi All..... my XC90 performs faultlessly in every respect.
No knocks, bangs, squeaks, or any anything untoward from the engine, gearbox, suspension, brakes, diffs etc.

I have taken the car offroad a few times (Sand) and there is no issues with the AWD.

BUT..... There is a resonance that fills the cabin when i decelerate. It only happens @ 1200rpm to 1800rpm and between 75km/ph and 90km/ph but peaks @ 1500rpm and / or 80km/ph.

It fills the cabin but there is no vibration to be felt, just this loud resonating buzz (not a wine or a vibration) and it makes the kids feel sick when on our daily commute i have to sit for 5kilometers, going downhill at 80kmph @ 1500rpm.
If i take the car out of gear it still does it and if i start accelerating it stops.

I have checked all the heat shields that run under the car and they seem fine, there doesn't seem to be an issue with the rear engine mounts.

Anyone else found this problem? If so, what was the solution? Car is a 2010 D5 Executive with 7 seats and running Pirelli Scorpion Verde tyres.
 

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Have you checked your belt pulleys?
 

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-There is a resonance that fills the cabin when I decelerate.

-It only happens @ 1200rpm to 1800rpm and between 75km/km (45mph) and 90km/hr (55mph) but peaks @ 1500rpm and/or 80km/hr (50mph).

-If I take the car out of gear it still does it and if I start accelerating it stops.

-It fills the cabin but there is no vibration to be felt, just this loud resonating buzz.

Pulleys, huh?

edit- add some bold
 

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Ah, crap. Here we go again...

Since occurrence changes due to engine RPM, I first think that it has to do with something that changes speed with engine RPM. First thought-wheel bearings? Rotors? Then, it repeats the sound when the car is taken out of gear, which means that it can't be related to wheels or anything post-transmission. Acceleration means a change in RPM and probably is leaving that range of RPM in which the sound occurs, therefore again tying the issue to something RPM-related. Lastly, I have a similar heavy buzzing noise issue which you put down as "it's probably nothing, if the exhaust isn't leaking why worry", but I am now starting to diagnose is one of the pulleys going bad. The same symptoms are present with my scenario, which is NO vibration, but instead a loud, deep, "resonating" buzz.

Don't want to go onto the same tangent that you went on in ChitownV's transmission fluid thread, but I think that it's time to start contributing to threads for reasons morally greater than putting others down or negating what they say. Everything I say and write is fair game to be held against me in terms of "false information", sure. But that doesn't mean I'm inviting others to be condescending when it comes to disagreeing, which is something that can be accomplished with a simple "Maybe it's not the pulleys, I'm thinking...<insert your idea of the cause of the issue>...". Don't get me wrong, I have great respect for you and everyone else here that is a "veteran" SS member and the experience people like you bring to the table with Volvos. But actions like this just defeat the purpose of it being a public, open forum.
 

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Dude, you're talking out your butt. That's it and that's all there is.

edit- return original post
 
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-There is a resonance that fills the cabin when I decelerate.

-It only happens @ 1200rpm to 1800rpm and between 75km/km (45mph) and 90km/hr (55mph) but peaks @ 1500rpm and/or 80km/hr (50mph).

-If I take the car out of gear it still does it and if I start accelerating it stops.

-It fills the cabin but there is no vibration to be felt, just this loud resonating buzz.

It's the resonance with the lack of vibration that's got me thinking. Anyone else want to make a suggestion?
 

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Mounts are new and/or fully functional? No chance the engine is tipping on deceleration and you have a compromised exhaust that presents a specific drone on the RPM you're noting?
 
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My '09 3.2 had a weird hum-resonance-vibration when I first got it. It only happened when driving on the "float", neither accelerating or decelerating. I didn't think a lot about it because it wasn't something that had the characteristics of something that would have me exercising my AAA card. Let it go for quite some time, and then one day I grabbed the the upper torque mount strut and gave it a wiggle. I was surprised that it was loose and rattly. It's the part that is shielded from view by the engine end mount. I pulled the thing off and saw that the engine end mount was compressed and loose in it's journal. I filled the spaces up with black silicone gasket goo and let it kick overnight, while I ordered a new one from FCP. That familiar noise was gone.
 

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I thought about this some more.

Droning (resonating buzz) but no real vibration felt between 45-55 MPH and peaking at 50MPH (easier for me to noodle than kph). With the resonance and droning only on deceleration, whether under powertrain load (D) or not (N).

If you take the car out of gear, it still does it. Ok, if you take the car out of gear the RPMs go down immediately so guess this would be a speed thing and RPM would be a secondary input. I’ll self-correct my earlier assumption of a mount. and/or a leaky exhaust if that's true.

And you said 2x that there’s no vibration to speak of, just a droning resonance sound that fills the cabin (XC is unibody so everything fills the cabin).

So for me, next test might be to get it to drone in gear and then “feather” the pedal a bit (light touch), see if there’s a specific point in re-applying power that the sound goes away with any observations that go along (like a feeling of engagement as example).

Last but not least, just for my own sanity, do the same general acceleration/deceleration test but during the drone, steer the vehicle in a turn. Does not have to be abrupt but you want the vehicle load to shift. Do this both left and right, see if there's any difference n the drone.

Thanks
 

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Discussion Starter #11
Hi everyone.... Thank you ALL for suggestions and thoughts.
I will pull the car out the garage this weekend and further investigate all the avenues that have been suggested. And update.

In relation to being a lack of vibration - Put it this way, if i have the stereo turned to the same volume as the resonance, id never know it was happening at all. But turning up the stereo isn't my long term solution :ROFLMAO:

Again, thank you all!!!
 

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Are the windows in the rear doors open?
 

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Are the windows in the rear doors open?
:D
I hate that coke-bottle whoom-whoom-whoom. So many cars have that, as I've found out from renting cars.
My theory is that it started when rain gutters were eliminated.
 

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Our GLS450 has wing windows in the third row. If you open them it goes away.
 

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Discussion Starter #15
Ok. Just taken the car for a drive on some hilly roads to test different scenarios.

1. Having any or all of the windows open or closed makes no difference.

2. It's the speed and not the revs that seem to cause the resonance.
**80kph at 1500rpm in 6th gear (off the throttle) and the resonance is there.
**80kph at 2200rpm in 4th (off the throttle) and it's there.
**In both of the above scenerios just the slightest press on the throttle and the resonance goes.
** If I'm at 80kph and in in neutral the resonance is there and doesn't disappear no matter how much I rev the car.

3. Making lane changes (steering input s left and right) makes no difference.

4. Going under an underpass and deceleration from 90kph down to 80kph and the resonance in the cabin that comes on at 80kph doesn't seem to be a noise that can be heard outside of the car (from the outside the car seems to make the same noises at 80 as it does at 90.
 

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Bad bearing somewhere in the final drive train (after the transmision reduction).
 
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