My kitty has an odd noise that occurs intermittently only at speeds greater that about 40 MPH and under a light acceleration. From my listening point in the driver's seat, the origin seems to be behind me centered under the rear seats. It is a light sound, like a metal rubbing on metal. It is not a grinding sound.

I suspected something in the drive shaft / u-joints / differential but my independent mechanic went through it and hasn't identified anything wrong. He's heard the sound too and told me the intensity isn't anything to worry about (for now).

I don't like things like this as it shouldn't be making this kind of noise and I'd like it corrected before things get worse. For sure Murphy will raise his ugly head on my next trip to Las Vegas (Dec 23rd) right in the middle of Nowhere, Arizona (a real place BTW) and have the back end of the kitty fall onto the highway.

So, can the collective minds of Jaguarforums.com come up with a diagnosis?

Thanks in advance!
Scott

 

These cars have grease fitting on the rear end half shafts that seldom get serviced even though the manual says 10k miles. Start there.

 

I'll ask about that in the morning when I go to pick it up. This guy is supposedly a Jaguar specialist. It will be a good test!

 

Yes, a worn out ujoint can make a noise, but it usually happens when you first accelerate. to me I would say put the rear up on stands or a lift and start the car and run to over 40mph, my bet would be you are low on fluid in your rearend(not that rearend) or maybe the rear tranny crossmember is loose or the rubber mounting is broken.
I disagree with your mechanic, no noise in the drive train should be left unchecked. I lost a seal in my vette rearend, you can imagine my surprise when at 30 mph my rearend locked up and I skidded to a halt, lucky for me I was slowing for a light and no one was behind me.
Check for fluid leaks around the tranny tail housing and your center chunk (rearend where driveshaft connects to rearend).

 

You and I certainly agree that the noise should not go uncorrected! Thanks for your input, I'll go over this and the previous recommendation with the mechanic in the morning.

Again, many thanks.
Scott

 

Did you ever figure out what it was? I have a similar situation.
Mine is in a 1997 XK8. Let off the gas and kitty rolls smooth.
Lightly accel and it is an annoying metallic scraping sound.

 

No, we haven't figured this one out yet. There's another thread (search for a thread containing "interresting" in the title - yes the spelling is unique) which has lots of additional information.

However, now that you ask, I have an update on the symptoms: Originally this only occurred while accelerating under light load between 40 and 45 MPH with the transmission in "granny mode" (not sport mode). I had not had the symptom in sport mode. A few weeks ago while driving up the Cajon Pass (I-15 toward Las Vegas from San Bernardino/Riverside) in sport mode, the same noise was heard but this time only around 65 MPH.

Somehow in my mind this would not be a U-joint problem as the symptom changes with the transmission mode.

Any thoughts? Gus???? H2OBoy?? Reverend Sam??? Others???

 

My car had a similiar noise and under the same conditions. It turned out to be the rear flex coupler in the tranny was cracked. Not a good thing and pretty expensive to fix.

 

Thanks Itspec! I'm going to be lazy and not look this up right now but I'll ask you. Is this flex coupler contained within the tranny case making it difficult to inspect? How did you go about finding it?

Scott

 

Not sure on this but could the forward drum in the trans failing act like this? Also if the noise is in the rear might be worth checking the parking brake shoes behind the rotors.

 

The flex coupler is behind the transmission, part of the drive shaft. Many cars have a cracked one, few get replaced because they usually do not cause a problem.

 

Do you mean a "center carrier bearing"? My 77 XJ6C had one that got damaged and needed replacing, but I can't remember what it sounded like. It's a yoke with a heavy rubber isolater around an actual bearing that the driveshaft goes through. I wouldn't think a shorter car like the XK8 would need one but maybe it protects both gearboxes from all that humongous torque we apply.

 

One piece shaft with a jurid coupling, instead of a universal joint, at the forward end. Here's one @ eBay: eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices

 

I made a mistake in my post..it was not a cracked flex coupling but the bearing in the tail of the transmission that was cracked and needed replaced. That's what was making the grinding sound. I got my bill out and reread it. The shop found the problem by putting it up on a lift and running it at various speeds.

 

Not a problem! Thanks for doing the research.

It seems, based on forum responses, this symptom has multiple potential causes. If you haven't read the related posts, I've had this to two different Jaguar dealers (Royal in Tucson and Gaudin in Las Vegas) as well as my local independent shop.

Gaudin found the motor and transmission mounts were out of sorts. The tranny was sagging and we hoped replacement of the mounts would straighten things out. While everything is nice and perky now, the noise still persists.

Royal found and fixed a few other minor things (missing bolts in a bracket, misaligned heat shields, etc), however the problem still persists.

The noise is difficult to reproduce on a lift (we even tried dragging the brakes to create a load) and the next step would be expensive tear downs. We've decided that since I've got seven months left on an extended warranty (which doesn't cover diagnosis) we'll let this go a while longer to see if the problem becomes more persistent. My only worry is something utterly failing while on a road trip.

Meanwhile, I keep working with this wonderful forum looking for others who have been through this and solved the riddle.

Personally I keep going back to something in the transmission as the MPH required to create the sound changes depending on the transmission mode (40-45 MPH in granny mode, around 60MPH in sport mode). If you take the transmission out of drive and put it in fourth, the sound does not occur.

 

What you just stated means it is an engine related noise as the rpm needs to stay in a specific range.

 

My gut doesn't think so as the noise seems to come from well behind the engine. However, it could also be something I ate for breakfast.

I haven't watched the tachometer to see if it is the same RPM whether in sport or non-sport mode. I will now.

Thanks!
Scott

 

When you change gears and have to adjust ground speed to 'hold' the noise you're actually maintaining engine rpm. If it seems to be coming from behind the engine at a specific rpm you might suspect the exhaust.

 

Good thought, I'll keep that in mind as well. I only puttered around town today and didn't get up to the higher speed in sport mode to see what the tach reads. In non-sport mode (I'm not calling it "granny mode" any more as I'm married to a "granny" and she drives a supercharged Bonneville like it should be driven), the tach shows around 1600 RPM during the buzz.

Hey Reverend Sam ... what does your tach show during your buzz???

 

Has this noise been found by anyone yet as mine is really ruining the drive to work, and i'm slowly deafening myself by having to turn up the music, Harmon Kardon sound system does sound good though.!!!