I've had my 2001 Blazer for about 20,000 miles now (currently has about 112k) and am wondering about a humming noise that has been present since I bought it. I'll go ahead and say that I thought it was my fuel pump but I just replaced it on Friday with a brand new Delphi and it didn't take care of it. (Note: that isn't the only reason I changed the fuel pump; it has been very sluggish up hills and has had some starting problems after sitting a while and the new pump cleared those issues up. I was just hoping the noise would go away with it.)

Anyway, after I get up to about 40-45MPH or higher then there is a loud humming coming from the back of the car (at least that's where it seems like it is coming from). It only does it while I have the gas pedal down (even just slightly) and as soon as I let off the gas it stops. The tires are in really good shape and aren't an aggressive tread pattern so I don't think there is any chance of it being road noise from them. The only thing I can think of is maybe the U-joint at the rear axle? I'm not very familiar with how it works while you're moving but if the driveshaft stops spinning when you let off the gas pedal then that U-joint would make sense I suppose. Otherwise I'm not sure what else it might be since everything else I can think of would be constantly moving and wouldn't be affected by me letting off the gas pedal.

My girlfriend seems to think the Blazer she used to have made the same noise so I guess it could just be something they do but this is the only Blazer I have owned and I haven't paid much attention when riding in others in the past.

Thanks for any help!

 

Easy way of checking you u-joint is getting under the truck to where you can see the u-joint and look at it then move the drive shaft by hand and see if there is play in the u-joint. If looks good and no play your u-joint is most likely good. My opinion, if noise is coming from the back, would be to take your diff cover off and look around in there. Check the gears and stuff for abnormal wear.

 

I understand you don't have aggressive tire tread, but a separated belt on a 'street tread' tire will make a lot of noise. Try rotating the front tires to the rear and the rears to the front. Not in a X but straight back, if you know what I mean. If the noise moves to the front, one of the front tires has an 'issue'. Now back to the mechanical noises. First I want to ask that you always post the pertinant info on your Blazer like 4WD or 2WD, auto or manual, and so on. It is easy to put this info in your signature so you don't have to remember to type it in each time. Chevys have had a problem with noisy differentials. Check it for fluid level and if it is getting too warm after a drive. It could also be a hub wheel bearing going out.

 

You know, mine does the same thing since I bought it. Dont pay any attention to it

 

Sorry, it's 4WD with an auto trans. Also a 2 door if that makes any difference.

I have rotated the tires several times since I have owned it with no change in the noise and I have had it on a balancer to verify there aren't any separated belts.

 

I believe driveshafts are balanced also, maybe?

 

had a "U"joint in a full size truck that had two of the rollers rusty. Slight humming noise. Mechanic buddy said they were fine, pulled them anyway (200,000 miles) and the problem went away. Dirty job, but not too expensive.

 

I was under it yesterday and it seemed tight so it could be an issue of rust. I'll have to get it taken apart and check it out soon. I spent all weekend doing fuel pump, shocks, cv shafts, sway bar links, and ball joints so getting back under it in my driveway does not seem very inviting at the moment.