At highway speed I am hearing or feeling this rotational faint droning noise and for lack of a better discription it is like vroom vroom...and so on, it is not getting worse but is always present. Recently at say 35 to 40 miles/hr and about 1400 RPM or so and the car is crusing and I give it a little trottle I get this vibration it goes away when I pick up speed. I was told by a reliable source that it is an exhaust resonation and by putting counter weights on the catalitic converters the resonance will go away. Has anyone heard of this. It sounds plausible but am not sure what these weights would be or how they would be installed. Hopefully someone will tell me I am not going crazy.

 

there's a thread on the UK forum about this issue which seems to confirm the "cat band" theory:


http://www.jaguarforum.co.uk/viewtopic.php?f=52&t=26181

 

I was feeling a drone at 1350 rpm, brought the car in to the dealer after searching the net and finding that it was a known issue. I had this modification done to my 07. Service was detailed as:

309107 Mounting Bracket Modification for Pedal Box Noise. Two part numbers: C2P13477 and C2P13478 (Bracket Mounting). This was done under warranty.

I would say that 90% of the objectionable harshness left with the repair.