Noise driving me nuts

My money pit of a truck, 99 S10 ZR2 66,000 miles has a noise that just wont die. It really sounds like a wheel hub hum but just I replaced both hubs, the right side hub bearing was bad and the noise completly went away for two days after it was replaced. Now the noise only happens between 60 to 65 MPH, same tone as before but is MUCH softer in sound, (sounds like it did when the bearing first started going bad, I can actually hear the radio now), no change in sound when shifting the trucks weight from left to right but when I go over a hill it gets much louder, goes away in the valley of a hill. It has gotten colder here, below freezing since replacing the bad hub a week ago. When the 4WD is engaged it almost goes away but can still be heard if you listen closely over the extra noise the 4WD makes. I've resently replaced the halfshaft on right side (cracked CV boot, clicking noise), 4WD vacuum valve, both hubs. I checked the left halfshaft last night turned the steering both ways while on a jack, no clicking sound and no slack. I've read most all the posts that relate to this noise but have only read a couple that actually solved their problem. My question is would it be possible to have gotten a defective hub? Or do you think the other halfshaft (left) might be bad, since the noise gets louder going over a hill and goes away when weighted by Gforce in a valley of a hill. I did replace the left inner CV boot a couple years ago and could have been damaged my moisture? I really don't think the problem is in the transfer case even though the vacuum switch did go bad and was replaced. Thanks for your help, all opinions will be appreciated!!!

My money pit of a truck, 99 S10 ZR2 66,000 miles has a noise that just wont die. It really sounds like a wheel hub hum but just I replaced both hubs, the right side hub bearing was bad and the noise completly went away for two days after it was replaced. Now the noise only happens between 60 to 65 MPH, same tone as before but is MUCH softer in sound, (sounds like it did when the bearing first started going bad, I can actually hear the radio now), no change in sound when shifting the trucks weight from left to right but when I go over a hill it gets much louder, goes away in the valley of a hill. It has gotten colder here, below freezing since replacing the bad hub a week ago. When the 4WD is engaged it almost goes away but can still be heard if you listen closely over the extra noise the 4WD makes. I've resently replaced the halfshaft on right side (cracked CV boot, clicking noise), 4WD vacuum valve, both hubs. I checked the left halfshaft last night turned the steering both ways while on a jack, no clicking sound and no slack. I've read most all the posts that relate to this noise but have only read a couple that actually solved their problem. My question is would it be possible to have gotten a defective hub? Or do you think the other halfshaft (left) might be bad, since the noise gets louder going over a hill and goes away when weighted by Gforce in a valley of a hill. I did replace the left inner CV boot a couple years ago and could have been damaged my moisture? I really don't think the problem is in the transfer case even though the vacuum switch did go bad and was replaced. Thanks for your help, all opinions will be appreciated!!!

It sounds by your description that your front differential is attempting to engage. Check your vacuum actuator switch on the transfer case and see if the plunger is stuck in or is binding. The switch is located on the drivers side top and has 3 vacuum hoses going to it.

that or the bearings are shot again.

The noise getting louder as you are cresting a hil is a tell tale sign of a defective and failing bearing.

Where they ever serviced when you replaced the hub?

that or the bearings are shot again.

The noise getting louder as you are cresting a hil is a tell tale sign of a defective and failing bearing.

Where they ever serviced when you replaced the hub?

Yes, I replaced both hub/bearing assemblys (4WD comes as one unit with speed sensor).... funny thing, it was above freezing yesterday and there was no noise at all... seems like the only time I hear it is when it's colder...hmmmm? Thanks for the reply, I am leaning towards a defective hub/bearing but it's really hard to nail down what it is without shotgunning parts and they don't come cheap. As far as the transfer case it has a cable that goes under the battery but the vacuum switch was just replaced.

Hmmm....

That is indeed strange.

Have you ever had the front differential fluid changed ever?

Hmmm....

That is indeed strange.

Have you ever had the front differential fluid changed ever?

LT, it is still gettin' creepier (is that a real word?). He ought to think about changing it out. Sounds as though it's freezing and there is only one thing that will do that.

When you replaced your hubs did you torque them to 180 ft pounds preload? (while still in the air) If not you could have under or over torqued them and they could be going bad again. (can happen withing a few miles)

did you by chance bend the dust shield?

No, I've not changed the fluid I will do that ASAP, good idea that makes sense. Also I don't have a torque wrench and it is possible that I over did it. Both are good ideas and very helpful. thanks!! BTW it was 10 degrees F this morning and the noise came back but took almost 20 miles before I heard it.

Sounds like you over/under torqued the hubs... Grab a torque wrench from pepboys/autozone on their loan a tool program, get new hubs (if they were over/under torqued they're hosed, I.E. Ruined) and re do it properly. Remember, the 180 ftlbs has to be done preload (while the wheel is off the ground).

That's why I don't like working on my own vehicles anymore, too much stuff for me to screw up...haha. When faced with a 1200.00 dollar repair bill VS 300.00 to do it myself I did the logical thing... Oooh well I can still do it over and still be money ahead. I will have to say this is one of the worst designs for a wheel bearing I've ever seen I hope the engineer that did this design no longer works for GM. I think before I redo this job I'll try and torque the nut the right way and see what happens... who knows I might get lucky... yeah right..haha. Thanks for all of the help, I'll let you know what I find out!!!

Remember to jack it up before you torque it

bevieve it or not I was very close to 180fp by guessing the torque when I first installed the hubs (+- 10 pounds).. I did jack it up preloading it.... ok now onto the fluid, I'll keep you posted... thanks!!!

Ok
If the noise does not change when you shift the weight of the truck like doing small quick turns from left to right then its NOT the front hubs. Also you said the noise does CHANGE when 4 wheel drive is used. I would start looking at the front diff. Are the front dif axle seals leaking????

no they aren't leaking I've checked that when I was replacing the hubs. I do plan on changing out the front diff fluid and will look for metal shavings... other than that it leaves me with a defective hub or CV halfshaft. The noise is the same tone as when I replaced a bad hub/bearing but MUCH softer............ If I find out the diff is ok, then I guess I'll leave it alone until what ever it is fails, I have a year warranty on the hubs.... thanks again

if it were the cv halfshaft you would hear a noise while turning, like a clicking or soft grinding. Also, you may not have a drain plug on that front diff and there is no cover to remove like the rear (must have been that same GM engineer). Get a good metal suction gun from the auto parts store, they are not too expensive, and make sure you suck as much out as you can. The manual should tell you how much oil is in there. Good luck.

get your tires balanced