I just woke uo this morning to take my wife to her training class and while I was driving my 04 S-Type V6, with 96k miles, began making a sort of humming or rattling noise. It is not a constant noise, more of a noise like when you go outof highway lanes and your tire is in the shoulder, like a buzzing noise. The noise seems to come from the rear of the vehicle. It had new tires and a balance done about 6k miles ago. I thought about it being a bearing but the noise would be constant. I also thought about it sounding like pressure release valve on the a/c compressor when you put to much free-on but it is coming from the rear. Sounds louder as the mph increase and is hear from 1.5 rpms to 2.5 rpms.
I'm thinking of rotating the tires later, if I don't get any suggestions I will got to mechanic shop and post results.

 

How much gas is in the car? My Fords have always made anoise from the rear when low on fuel and the pump is getting old. Filling up makes the noise go away.

When was the last time the rear diff fluid was changed if ever?

 

I would rotate the tires and see if the noise moves around.

 

Gas wise it has 3/4 of a tank and it never goes pas 1/2 before I fill it up again. As for the differential I really don't know if it was ever replaced but I have pick I would like to show you guys. I founda plastic piece, seal thing broken in th rear of driveshaft where it mets the differential I also found a couple of boots that where ripped I will upload pics.

rear seal of driveshaft

 

Front drive shaft seal looks fine

 

here are the ripped boots

 

Also the mount of the differential is fine no cracks

 

I don't think the ripped boots would cause a noise. Maybe a vibration or sloppy handling, but I doubt about noise. I would look more at your first pic. Is that where the driveshaft meets the diff?

 

yes it is where the drive shaft meets the differential.I actually just came back from the rotationand I noticed no change but I did notice that the rpms lower a bit when the noise starts. I shifted the engine to neutral and it doesn't do it in neutral, don't know if that helps but I think it eliminates the gas pump

 

Here is the possible options

 

Well I went for a drive and it sounds like a semi using air brakes but of course not that loud. I put in neutral and reved it to 4k rpms and it didn't make the sound I also was driving at 55 mph and also put it in neutral and the sound didn't come back until I put it in drive again I am going to leave at mechanic. I also drove it at wide open throttle and it reved to 6.5k rpm fine. Don't know what is up?

 

Spoke with mechanic bearings good, pinion seal good. tires have a small flat spot, will be towed to tranny shop tommorrow.

 

It also started shifting hard from 2nd to 1st..

 

the boots rip due to the heat.. have gotten lots of cars from florida.. that all the bushings in the rear are cut or torn open

 

Any suggestion on the buzzing sound maybe I should post a video ..... and tranny guy said he doesn't have the special tools to look at Jags tranny