So recently my 1999 Blazer LS 150k miles (automatic) has been making this unusual noise, upon acceleration the noise will get higher pitched and less loud, once i start to decelerate and starts slowly going down to a low pitch and gets very loud then theres a *THUMP* it sounds like it's coming from the front axle or something, could anyone diagnose this?

Video of the sound:


Also it's been insanely cold here -10 - 20 degrees on average, and what do you know my heat randomly stopped working! I still have ac, the air still blows, there's just absolutely no heat. I then realized my engine temperature gauge was not working at all, could this mean the thermostat is broken and thus causing it not to make heat?

Thanks in advance for your help.

 

Sure sounds like a bad wheel bearing. Does the noise change if you turn the steering wheel, like on a freeway exit ramp?

Could be a bad thermostat. Are both heater hoses hot at the heater core? Is the upper radiator hose hot?

 

Is it a 4X4? If so, it'll have the same hub bearing in the front as the rear in my Corvette.

Elaborating on what the Captain said, try this:

Use common safety sense, like on an open highway with no traffic around:

Get up to speed on a strait away and quickly jerk the wheel to the right (and quickly back to the left so you don't wreck). Sound go away? You most likely have a bad right bearing hub.

Do the same for the left side as well.

I did have a friend with a FWD Ford and the test above was opposite. The sound went away quick right, and it was the LEFT bearing that was bad.


So....

You can also jack the tire off the ground and place your hands at 12 and 6 o'clock. Try to rock the tire back and forth. Should be minimal movement. Since you have the tire off the ground, rotate it (if you can) to see if you hear the strange noise. Do both sides. I once had a brake shield rub the hub causing a similar noise. A quick bend by hand took care of that. I also remember my Mom's Chrysler 300 made a bad noise, and a rock was caught between the brake shield and disc. Also, are you sure it's coming from the front? Had the same sound last summer and it was the rear axle bearing shot, but the sound was clearly from the rear. Also, after driving it a a bit, feel around the hub. Hot? another sign of a bad bearing.


Also, with the car in neutral/park, rev the engine. Hear the sound? If so, forget all the above, it could be a failing water pump (contributor to the no heat) or any other accessory/motor bearing.

I recently flushed my heater core and got my heat back.

Hope this helps, and let us know.

Thanks!

 

There are two sets of ball bearings in each hub, (inner and outer). They quiet down when they are unloaded. If the sound changes when you swerve back and forth, it confirms that a bearing is bad. Sound travels, and identifying its origin can be very deceiving. Best to use a stethoscope.

 

I think wheel bearing

 

as the other posts probably wheel bearing.now your heat I would try new thermostat.also there are 2 lines coming out of firewall that run to your heater core.if you pull them off and use a garden hose to flush any sediment in there.