Since changing the crank pulley and the aux belt and tensioner on my 2003 x type 2.0 diesel it has been making a horrible rumbling sound particularly when idling and when cold.This has driven me mad with frustration for 4 weekends as although it’s loud it’s been hard to pinpoint the exact problem.I thought it could be that the main aux belt was a cheap replacement from eBay.To confirm this I got a second hand tensioner from breakers and fitted it.It did seem very slightly quieter but still not anywhere near satisfactory.Today it sounded particularly bad so I turned off engine and with a metal bar I pushed down on the aux belt.I realised that it was very tight, probably too tight in fact. There is no adjustment on the tensioner so just to confirm my hunch I removed the 10mm bolt that fixes the large spring (the shock absorber type thing) to the engine).As I thought the bottom of the spring dropped about quarter of an inch and this resulted in a small amount of give on the belt.When I started the engine It was 99 percent quiet.Ihave driven around like this for a good few miles with no bad effect.I can only conclude that the belt I bought,also from eBay , was slightly too small .I remember it seemed a bit too generic as it listed various other makes of cars it could fit.I am going to buy another belt this time from Jaguar . I will also then re fit the 10mm bolt.All should then be well.If you have this problem I hope this helps cos it nearly had me beat.

 

Good result and thanks for sharing.