ODD wump wump wump noise dead on 70MPH

[aircooledfool]

I got the old thing up to 70 today for the first time , at first I thought I had left a window open as there was a repeating "wump wump wump" noise , you could actually feel it as well, not horrendous just slight, does not happen at 68 MPH just at 70 and does seem to be at the rear. Next thought was tyres , I checked them and they are all good and at right pressure. Local Indy jag specialist  at a loss , they have never seen this before. An Jag owning acquaintance  suggested that this is caused by airflow over the tail gate lifting the tailgate because the seal is worn .  Don't fancy this idea much as the seal looks in good nick and there is no discernible movement in the tailgate once it closed. Next move is to swap the wheels front to back  and see if it tranfsers  the noise to the front  , but clutching at straws  , i think

Any one seen this kind thing before ???

[JOE-DOT-COM]

Hi

It could be the tyres

I would try swapping the front tyre's with the back and see if the noise shifts

they are a common cause of this type of noise

cheers

Joe

 

 

[aircooledfool]

Changed the wheels around today, and there was some difference , Noise is still there but definitely reduced. I don't really know how much noise you would expect from an X type with a few miles on it (around 80k). Could be that I am hearing "normal" transmission/tyre noise. However , I would expect it to be reasonably quiet at motorway speeds. It is not so difficult to change the diff but I think that if the diff was noisy you would hear it a various speeds, not just one (70mph in this case) In the end given that the rest of the car is in VGC, perhaps it is just a bit more noisy than I expected. I know that tyre choice can be an issue and some brands will increase road noise so I will look around the website to see what people say about what tyres to go for. A reply on tyre knowledge would be appreciated. 

[aircooledfool]

Changed all tyres for GT radials sport active, noise not quite gone but much better, car just gets a bit more noisy around 70mph , then noise goes after 75mph. Noise is much reduced after new tyres and is no longer a pulsing noise 

Tempted to just leave it now failing any response that might help