[RatPatrol]

Hi all. First post here.

I have a 2002 OBW Base. H4 with automatic trans. 144k miles.

Today it began making a rhythmic grinding noise that sounds like it's coming from the rear of the car:

-Varies with the speed of the car
-Gets louder during left-hand turns or as the suspension is loaded, such as going up from a dip in the road. Conversely, it gets quieter as the suspension is unloaded or when turning right.
-Only happens while maintaining a steady speed or decelerating - it goes away when the brakes are applied though.
-I don't really hear it during acceleration
-It will also go away if I gently apply the handbrake while driving, even when applying more gas to maintain a steady speed.
-As the car comes to a stop (like at about a walking pace), the grinding noise becomes more of a thunk, still relative to vehicle speed.
-I can hear a light, metallic scraping noise when idling along in D, again, relative to vehicle speed.

Though it gets louder when turning left, I don't think it's a bad bearing as it came on suddenly during my commute home today and it's not the droning growl I've heard when a wheel bearing goes bad in other cars.

I've did some searching, and it sounds like it's either a bad drive shaft u-joint, a bad CV joint or the rear diff having issues. I haven't jacked the car up yet, but it looks like the CV boots are in tact. Admittedly, I only took a quick glance under the rear of the car.

If it's a bad u-joint, will there be any visible signs, or will I need to disconnect it to make that determination?

I don't know when or if the rear diff fluid has ever been changed, and I haven't yet checked the fluid level.

The outer surfaces of the rear brake rotors are smooth, and the rear calipers aren't hot to the touch.

I appreciate any advice you might have.

 

[rasterman]

Pop open the underhood fuse box and insert a spare fuse (any rating) into the FWD slot. I think that's the frontmost fuse slot; normally unoccupied. You should see spare fuses clipped inside the lid of the fuse box.

This will override the AWD system and temporarily convert the car to FWD. You'll get a light on the dash to confirm this.

See if it changes the noise pattern. You're locking out the entire rear drive system with this, so if the noise changes substantially or goes away you've confirmed that it's something from the propshaft back.

 

[RatPatrol]

Thank you for the tip. I'll give it a try today.

 

[1 Lucky Texan]

could be parking brake parts related, but that is uncommon.

 

[AWDFTW]

Likely U joint. Potential wheel bearing. Rear CV issues are pretty uncommon unless some sort of strain/damage has occurred. Same for rear diff.

 

[RatPatrol]

I popped in the fuse to disable AWD, confirmed 'FWD' was illuminated on the dash and the sound was still there.

After listening to it some more today, from the inside of the car it's more of a clunking sound rather than a grinding sound. With windows open, I can hear it as a metallic scraping sound echoing off curbs and parked cars.

My daughter put her ear to the back seat and says it sounds like it's coming from the driver's side.

Time to jack the rear up and take off the the wheels.....

 

[eagleeye]

wheel bearing,

brake backing plate, (the stone / dust guard)

too much debris in brake, separating brake pad.

 

[RatPatrol]

Fortunately, it turned out to be a very simple (and embarrassing) fix. Three of the lug nuts on the rear driver's side wheel were loose. Barely finger tight. I hit all four wheels with a torque wrench and found a few more that were under-torqued.

A few weeks ago, I had a tire patched and a rotation done at Costco, and I neglected to re-torque the lug nuts after 25 miles per their recommendation. Lesson learned there. I'll be getting in the routine of checking these on a regular basis.

Thank you all for your advice.