Diagnose sound....could be the hub or differential?

[Mr T]

Folks:

2008 Denali XL with 175K miles. Wife's car. I got in last week to drive us up to a cabin and quickly noticed a humming sound that appeared to be more from the front left (driver side) area. It increased in frequency as I sped up but when approaching freeway speed it became hard to hear over road noise. I was suspecting wheel bearing on front left side. Went back home and inspected under left side. Noticed left outer CV boot looked fine but had the circular grease patter all over the place, so its clearly lots its guts. Must be a small tear. So axle will have to be replaced. I repalce axle rather than just the boot since I don't know if this has run dry and not work the effort to find the joint is going..... That said, I don't ever remember seeing or hearing that a bad CV joint would be noisy on the road, rather you hear the clicking and clunking on turns. My noise is a humming--almost as if the tire is warn bad, which it is not.

My initial conclusion is:
1) Bad CV boot, which is confirmed. Will replace the axle, but this isn't the cause of the noise.
2) Likely bad wheel bearing or one going out.
3) Possible the differential is making this noise.

So I jacked the left front side and did a test to see if the hub is going. Up and down pressure has NO movement. Right and left has slight but that is the steering wheel turning. So the hub is intact and not lose. Also, I see no oil leaks from the differential. I have serviced the front and rear diff every 35K, so it's had full oil changes at least 4 times over the life of my Yukon. I know they can fail but I don't know what happens or how those failures are diagnosed.

My reason for this post is I REALLY don't want to replace my hub assembly if that isn't the culprit. I also have heard you can't confirm hub issues just by jacking all 4 and running the wheels because "GOING' bad hubs can be less noisy with no weight on them.

Any ideas from the forum to identify the humming sound? My wife called it a "turbine" noise, but it's not that high pitched. It is a whining, for sure, but hardly what I call a turbine.

OR would folks just replace the hub and go from there? I know they do start to fail and I have 175K in miles. Hard to know.

 

[Geotrash]

If your ears are good, which they appear to be, you can hear a wheel bearing going bad long before it develops significant play. It could be a differential whine, but since the hubs are easy to replace in these trucks when you have the axle shaft out, and new replacements are cheap, I think I'd replace it as a matter of course. If you have to tear into the differential eventually anyway, so be it.

 

[thompsoj22]

i also have some noise from left front wheel area. 08 xl1500 awd 130k miles. i refer to it as a "rum rum" most knoticeable on off throttle deceleration at slower speeds. comparable to a scalloped tire sound, just a dull rumble. i looked around and could not find anything that jumps out at me. there is quite alot of drivetrain slop involved with the transfer case to front diff and im wondering if when the drivetrain is unloaded that the noise is a result of the play in the system?

 

[Mr T]

Well, I did the big project today and replaced the left front hub assembly and front left axle. The axle was losing grease so it was on its way out. The nose is no longer there. I do have to say the old hub, when you turned it with your hands you could hear/feel it had a slight catch to it. So I'm rather confident it was the noise maker. Glad its not the differential as that is substantially more expensive.

 

[thompsoj22]

i also have some knoise from left front wheel area. 08 xl1500 awd 130k miles. i refer to it as a "rum rum" most knoticeable on off throttle deceleration at slower speeds. comparable to a scalloped tire sound, just a dull rumble. i looked around and could not find anything that jumps out at me. there is quite alot of drivetrain slop involved with the transfercase to front diff and im wondering if when the drivetrain is unloaded that the noise is a result of the play in the system?

update, after reading my own post "?" and realizing it maybe possible that a tire is making the noise i rotated them, did a tpms relearn and all is well the sound is gone. the tires had approx 7k miles in their position and from now on ill rotate at 5k.

 

[thompsoj22]

Well, I did the big project today and replaced the left front hub assembly and front left axle. The axle was losing grease so it was on its way out. The nose is no longer there. I do have to say the old hub, when you turned it with your hands you could hear/feel it had a slight catch to it. So I'm rather confident it was the noise maker. Glad its not the differential as that is substantially more expensive.

Any "ugly" aspect to the project or was it as expected?

 

[Mr T]

Yeah. Getting the axle to actually come out of the area, basically just removing it, was far more time consuming than I ever thought. I ended up removing the back-side shock bold as well as the stabilizer bar. Took me at least 1 hour to remove it. Putting the new one in took 1/4th the time.