I've been trying to figure out what's causing a loud humming sound between 65-75mph for the past three months or so. The past few days I've been thinking it could be that we lowered the rear end with the spring kit around the same time the hum started. Perhaps it has changed some geometry with the differential setup and caused some friction, or because the rear wheel wells are smaller above the tires they sound louder (including the Michelins)? Things like that.

I remember how we got rid of a very persistent buzzing sound from the drivetrain by replacing the rear tranny mount, not because we thought it would remedy the buzz but simply because the mount had collapsed. Another unintended result in a positive way.

Any other examples of results you have gotten that surprised you to the good or bad while trying to remedy issues would be helpful.

Racking my brain over this one!

 

After some digging, I found that there two ride height spacers in the rear spring assemblies. Top is 6.55mm and bottom is 3.4mm, which totals 9.95mm or .39in (3/8ths). If I went back to the origional springs w/o the spacers, it would lower the rear 3/8ths in. and possibily solve the noise problem.

 

Your ideas seem reasonable. Could it be that there is something (opening, flap, ???) in the well that is affected by the closer tire and 65-75 is just the right wind speed to make noise? Kind of like blowing across a bottle, it makes noise only within a certain range. I'd check the wheel well and see if there are any openings or anything loose and cover or secure it and see if it helps.

A simple thing I found on my tonneau cover pins - I had noticed that the clip on the cover appeared to have been mis-located on one side (which seemed exceptionally shoddy for a Jag). When clipped in the cover seemed offset a bit from where it should be. It didn't line up nicely like the other side. I thought maybe it was a replacement cover and somebody goofed in placing the clip. Thought I'd fix it someday. About 2 weeks after getting the car, I noticed there was a screw near the pin the cover clips to. Hmmm, wonder if the screw and the pin could be swapped.

Voila, in two minutes I seem to have returned those two little pieces to their proper places and made my cover fit properly. Looks like somebody had them out and just put them back in the wrong spots. I love an easy win.

 

It's more of a loud, harmonic tone or hum rather than a wind noise. It even puts a slight pressure on my ears at its loudest around 70mph. I think by lifting the rear end back up a bit the problem could lessen or go away.

The question I have is can the OEM rear springs function properly without the upper and lower spacers installed? I would at least like to remove the upper ones when reinstalling the oem springs so the car would still be lowered some.

 

Hmmm, seems like a compression/harmonic issue in the cabin. Changing geometry or providing pressure relief in the cabin should help. Does putting windows up or down change it?

 

Hmmm. I'm a bit skeptical of the rear lowering / hum connection. There have been lots of guys on this forum who lower the rear without this issue (including me).

Mark, I recommend you send a PM to Tony Murton (XKRacer) and ask him about this...he's lowered as many XK8s as anyone on the planet. If there's a connection, he'll have seen it at least once.

 

+1. My Rear Lowered Coupe has no unusual Noises/Vibrations.

 

Wrote Adamesh and reported the trouble and he said to check for all the spacers, collars, packers, etc in the spring assemblies. Jacked up the car this morning and found no lower spacers (3.5mm), and no upper spacers (6.5mm), so figured that the axle/diff relationship had changed too much and caused some instability. The shop is checking to see if there are some spacers floating around that may not have been put back in. If none can be found, I'll just get some and put them in. Should stop the nonsense.

Do your rear spring assemblies have the spacers?

 

Also worth checking the damper isolators are present / undamaged.

Graham

 

When the Jaguar Dealer installed the Mina Rear Springs in my car, they used whatever Spacers that were installed with the original Springs.

The (Very friendly and experienced) Tech did not indicate any addition/deletion of Spacers.

 

Same here, Skid. Spacers weren't mentioned when my springs were installed...I've got a pretty good tech and my assumption is that he used what was already there. No issues whatsoever, after several thousand miles.

 

rear bearing(s)? (geez, I hope not)

 

Tried raising the rear end about 1/2 inch today with spring spacers but didn't make any difference. Roar/loud hum was still there at 65-75mph. So much for my idea haha.

I've mentioned bearing roar to several people, I've wondered if it could be a hub or axle bearing. The thing about that is that it's quiet around town and doesn't start until highway speeds.

We are going to check the rear axles tomorrow to see if there is any binding or play.

 

Skid,

Hate to throw another variable into your equation, but have you considered tire wear?

Certain tires can get quite loud as they wear, depending on what you have. I had a set of BFG's on the wife's car a few years ago that began to absolutely HOWL after a couple of years, and only at certain speeds. As the tread blocks hit the pavement, certain tread designs can create a harmonic at certain frequencies (which are hit at certain rotation speeds).

Might not be your issue, but be aware that it can happen. See if you can rule it out.

 

Running brand new Michelins right now, but wish it was the tires. I like the new ride height though. Takes the highway bumps much better, no hopping or bottoming out.