Humming sound..can't figure it out..audio attached

mal81394 · Post by **mal81394** » 04 Mar 2018, 22:02

Hey Guys, I recently bought a 2010 XC90 with about 85,000 miles and overall love the vehicle so far...upgraded from an S60. The only issue I notice is that between 63-68MPH i hear a sort of loud droning or humming sound that is like this if you say it out loud..."nahhhhhnnnnnnnn...nahhhhhhh...nnnnnn...nah hhh"
It is a constant droning sound....but only at that speed and no other. Is this a common sound or is something wrong? Just replaced all 4 brakes so that isn't it and I also checked the hub while doing so and none had any play. Anyone here of this before or have an idea? It kind of sounds like it is coming from the front half of the vehicle if I had to guess. Absolutely no drivability issues or vibrations etc...any help would be great! I attached a video with audio..you can hear if you turn up your speakers...to get past the white noise.

mal81394 · Post by **mal81394** » 04 Mar 2018, 22:03

video of the sound

Post by **SuperHerman** » 04 Mar 2018, 22:14

I have the same noise in my 2004 - which has a different engine and awd system. As I have changed out the transmission, front and rear differentials, regreased the prop shaft, changed the front struts/spring pads plus an alignment and finally changed the motor mounts I figure it is either the CVs (which both look good) or the tires.

Have you tried rotating your front tires to the back? That is my next step.

mal81394 · Post by **mal81394** » 05 Mar 2018, 09:31

Interesting....and I am glad because I knew there had to be someone out there with the same noise. I just got brand new tires and the same noise is there. I haven't rotated them because they are all 4 the same brand new tires and the old tires did it as well. Does yours occur at the same MPH? What do you think about wheel bearing? Mine seem fine but I am not sure what else to look at???

Post by **SuperHerman** » 05 Mar 2018, 17:01

A bearing is what I also looked into, but usually turning from left to right would cause a wheel bearing issue to change noise as the load shifts. Mine does not change and the bearings check out fine. In addition a bearing would not have an oscillating sound - it would be constant.

I have read articles stating that it could be the tire construction. Have you tried changing air pressure to see if it makes a difference? What brand tires did you have and do you have now?

The thing I find odd is that the noise does not match anything that is rotating - that is the "beat" does not match or increase like I would expect with greater speed. Mine begins just over 60mph - very similar to yours.

I know that my XC90, which I have owned for over 100K miles, didn't start out with this noise so something is amiss.

On the other hand I saw reports that certain Lexus SUVs have a similar type of noise which is considered "normal".

Keep us posted on your findings, I will do likewise, but for now with the snow storm, I will not be doing much testing.

Oly850 · Post by **Oly850** » 05 Mar 2018, 20:53

I don't know if you have any urethane mounts on the engine or the rear diff, but this sounds like harmonic resonance which is why it's only presenting itself in a narrow speed / rpm range. If the mounts are stock, I'd check all of the existing motor mounts and the mounts on the rear diff. Bad gear lash would make noise all the time I would think. My $0.02.

mal81394 · Post by **mal81394** » 05 Mar 2018, 21:49

SuperHerman: I have not tried changing tire pressure. I have brand new cooper adventurer tires right now and did have a mix of pirelli and Goodyear. And yes your right it doesn't correspond to anything that rotates..it is a much slower rhythmic Hum. It would be hard to believe that this noise is normal so yeah I am not sure...keep me posted if you discover anything as well.

Oly850: I am not sure if I have the urethane mounts on the engine or rear diff but I guess it is worth a look. I looked up harmonic resonance...do you mean if the mounts are bad the engine vibrations are running through the frame making these noises? Or are you saying the bad mounts are making uneven gear mesh? I kinda think you are onto something here because the sound doesn't correspond to anything that rotates.

Post by **SuperHerman** » 05 Mar 2018, 23:09

I also like Oly850's idea, but on mine I replaced the front motor mounts - I think I put 4 or 5 new items up front with no change.

The noise seems to be from the front - but I suppose it could be something in the rear.

I will look into the rear diff mounts.

Post by **oragex** » 06 Mar 2018, 07:01

I am not able to hear a specific sound in the video provided, but I'd say that if you suspect a wheel bearing and go ahead to replace it, always turn the bearing by hand just prior to unbolt it - that is with all the brake assembly, brake disc and axle shaft away - just spin the hub by hand, it should feel smooth without any or with little rough points. Many times a tire would make the same sound as a worn bearing and we replace parts that are actually good (actually, mechanics do so).

If you are courageous, you can tape a go pro camera near sensitive points such as differential and record while driving. The rear differential also has an oil which would be good to have it replaced it by now.

mal81394 · Post by **mal81394** » 06 Mar 2018, 07:32

If you turn up your speakers you can hear a droning sound. I am thinking bow that it is not wheel bearings. Also, it does not go away if I let off the gas....this one is a tough one.