Hmmming sound

I have a 99' Blazer 4wd LT with 103k miles. For that last couple of weeks the car has been making a real deep hmmming sound that comes and goes every few seconds from the front of the car. It doesnt do it while in park. It only does it when in drive going about 20 or more mph. It almost sounds like it is in 4wd even though it shows me in 2hi. I have also been geting low gas mileage around 13 mpg and slow pickup... I have done a full tune up including spark plugs and wires, fuel filter, air filter, cleaned MAP, cleaned TB,and ran seafoam through the gas,oil,and pcv. Any idea's of what the problem could be?

Try the Search this Forum: Feature... Just type in "humming"

4wd is partially engaged.

while driving under 5mph, press the 4Hi button and then go to 2hi and back and forth 3-4 times to see if you can pop it back into 2wd only.

Well.. im thinking it might be the bearing in the front right because when i turn the steering wheel to the right while driving the sound goes away but when the steering wheel is straight or to the left you can hear it. Is the shaft going from the transfer case to the front differential supposed to spin while in 2hi?

Yip, it could be the right bearing.

Is the shaft going from the transfer case to the front differential supposed to spin while in 2hi or only while in 4wd?? I dont know much about 4wd cars and dont know to much about how the drive train works in them.

Is the shaft going from the transfer case to the front differential supposed to spin while in 2hi or only while in 4wd?? I dont know much about 4wd cars and dont know to much about how the drive train works in them.

Yes, it spins all the time, even when not in 4 wheel drive.

Whould the bad bearing in the front right cause me to be geting such low gas mileage or is it something else causing it?

It won't drop it that much.

I would take it to a shop for an inspection.

Unless they changed the t-case design since 89, the front drive shaft should NOT turn by hand when the truck is in 2WD. Correct me if I'm wrong.

Unless they changed the t-case design since 89, the front drive shaft should NOT turn by hand when the truck is in 2WD. Correct me if I'm wrong.

I was talking about when the car is in drive and moving the front drive shaft turns while in 2wd. Is it supposed to in drive? I have also noticed that it takes awhile for the car to go into 4lo and sometimes it wont even do it. And when it does go into 4lo when i put it in drive the whole car lungs forward. Does this seem more like a problem with my 4wd or the bearing in the front right? or both?

Throwing it in 4lo and getting the push forward, is normal, its in a low gear range, thats not a problem. You could have a couple of problems. First when you drive down the road, try turning the wheel a little bit each way(right and left) and see if this lessens the noise one way and not the other. If this is happening, then you do have a wheel bearing that needs to be replaced. The CV joints (axle shafts) turning with the wheel is normal-its designed that way. The second problem could also be that you have the front axle partially engaged. To know this, when driving down the road, when you decellerate, you will usually get a humming(maybe slight grinding) noise, this usually indicates a partially engaged front drive shaft.

Throwing it in 4lo and getting the push forward, is normal, its in a low gear range, thats not a problem. You could have a couple of problems. First when you drive down the road, try turning the wheel a little bit each way(right and left) and see if this lessens the noise one way and not the other. If this is happening, then you do have a wheel bearing that needs to be replaced. The CV joints (axle shafts) turning with the wheel is normal-its designed that way. The second problem could also be that you have the front axle partially engaged. To know this, when driving down the road, when you decellerate, you will usually get a humming(maybe slight grinding) noise, this usually indicates a partially engaged front drive shaft.

I think i might of used the wrong term. I was talking about the shaft that goes from the front differental to the transfer case. The humming sound does get quieter when i turn the steering wheel to the right so the right front bearing is prob bad. Its hard to tell if the humming sound is coming from the bad bearing or from it being partially engaged. I hear the humming sound when decellerating but it gets quieter at 15 mph or so.

I need to correct myself. The driveshaft that goes from the t-case to the front dif, it should turn by hand in 2WD. If it doesn't, the front axle coupler is probably stuck. The axle should also not spin while rolling down the road in 2WD. I should have this straight considering I just had it appart.

I need to correct myself. The driveshaft that goes from the t-case to the front dif, it should turn by hand in 2WD. If it doesn't, the front axle coupler is probably stuck. The axle should also not spin while rolling down the road in 2WD. I should have this straight considering I just had it appart.

The shaft from the transfer case to the front differental spins while in drive in 2wd and while in park i cant spin it by hand so i think that is the problem.What could be causing the front axle coupler to be stuck?