I have a 1999 XJ8L with approx. 80K miles. At 50K a remanufactured differential was installed under warranty. Approx. 5K miles ago a noise appeared which definitely sounds like a road noise. It started when driving up inclines and around curves. It seems now anything will trigger the noise. I've changed both inter and outer bearings at the rear wheels. Unfortunately, this didn't solve the problem. The noise is present intermittently between 45 and 65 mph, and never changes pitch. It seems to happen more on country roads than interstate highways. It's very hard to repeat the sound, but it can always be turned off with more or less throttle. There are no clunking sounds (shock bushings, etc.) I loosened the sub-frame bushes and inserted rubber vibration pads between any possible rub points, and retightened -- didn't make a difference. Bushings look like new. I've listened from the back seat and it doesn't sound as though it's coming from the drive shaft support bearing. I can't pinpoint either the left or right. It simply sounds like a very loud body noise.

One last thing I should mention: The tires have good tread, but are 10 years old. I've never heard of an intermittent tire noise. I've rotated them and it hasn't made a difference.

I would appreciate any suggestions.

 

You sound like you've covered the main areas. Have you checked the fluid in the differential? Also check the pinion for any play.
This may not seem feasible, but check your rear shock assembly, especially to top foam damper. If they are worn, you may be getting a driveline noise simply from the speed and lack of the damper to do its job to dampen the noise.
Look at this link on a '98 to see all that is there to make noise and what this repair entails....
http://jaguar.blackonyx.net/tech/rearshocks.pdf

 

I agree about the differential fluid, make sure it's full and that the breather is clear. Since it was installed only 30k miles ago it's probably fine, but I'd rule it out.

10 year old tires? My suspicion would be there.... Regardless of how good the tread looks that's a lot of years. I wouldn't let my wife drive a car we bought with 8 year old tires, even though the tread looked good. Honestly I'd probably risk it for me driving, but if she had an issue and I knew I could have prevented it, that would be tough on me.

 

Thanks for the replies. I have the car up on stands presently. My thoughts were leaning to the foam pads also. I've ordered rear shocks, and will be in the process of changing them. I'm going to take a look at the foam pads at that time. I'll also check the fluid and the input shaft for play. My plans are to change the 16" wheels to 18". My intentions are to clear up the noise before adding additional noise from lower profile tires. I realize the tires should be changed. Somewhere in the past I read an article from a tire manufacturer stating 7 years un-garaged -- 10 years garaged is the general rule. Thanks for the advice!