Squealing / whining sound under XJ

I've taken the XJ into two different shops on several different occasions in the past two-plus months with this recurring issue. They either can't figure out what the problem is and just keep telling me to drive it around until it gets worse, or they can't hear it at all because the sound is too high pitched for them. The sound almost goes away when the brakes are hot.

The sound (see link to video below) sounds like a metal lathe grinding at some metal. My first thought was a warped rotor or sticking caliper. It makes the noise when the steering wheel (at any amount of steering wheel rotation, both directions) is turned at lower speeds and when I press on the brakes while driving straight. When the sound comes about while driving straight, if I press on the brake pedal slightly, it's a constant lathe / high pitched sound; if I press harder on the brake, it gets louder very briefly, then the sound is gone.

Here is the list of things underneath that have been replaced at some point in the past year, some of which are [probably] not related:

- new brakes all around (Feb. 2015; brake lines flushed as well)
- new wheel bearing hub assemblies up front (Sept. 2014)
- new engine (Feb. 2015; threw a rod on the highway)
- junkyard front axle (Aug. 2014; blew out randomly one day in the neighborhood)
- junkyard rear axle (June 2014; kept hearing noises from the rear, metal shavings found everywhere)

Link to video: https://vimeo.com/129375133

Saturday, I took it back into the shop and they still couldn't see anything rubbing or worn abnormally. Driving the XJ in the city for the past two months, I would have figured that a rotor or caliper issue would be shown in the pads by this time but they still look brand new.

Any ideas?

I had also thought it could be the dust shield rubbing the rotor, but after coating it in yellow paint pen, I couldn't see any paint missing.

I had a disc brake mud shield dragging that made a horrible noise.

Your wife is in the house right? Jk

It may be caused by a bad differential pinion bearing.

I had to rig video camera to find my mystery noises. A bunch of duct tape to hold the tripod in place, facing right onto different suspect areas.

kippo1 said:

Your wife is in the house right? Jk

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hahaha. No gf [or wife] for me at the moment. I think I'd be broke having both a gf and an XJ.

tonytech said:

It may be caused by a bad differential pinion bearing.

Click to expand...

For a diff bearing, am I correct in thinking that a bad rear diff pinion bearing would whine while accelerating and the front diff bearing whine upon decelerating? If so, that could explain things especially since I am hearing the noise when I press on the brakes.

I went up under it today after work and tried seeing if there was any play in the yoke, where the joky meets the driveshaft. No play whatsoever. I'll have to open it up this weekend and take a look at the fluid and gears to see if I see any issues inside.

Do you think an axle shaft bearing could be causing this?