This thread is just for info really, until yesterday i was unaware that there are two different lengths of belt fitted to defender 300's. only 15mm different, but stil....
Some vehicles apparently have a small pulley on the alternator, and some have a slightly larger one, well, when i went for a new belt the specialist guessed which one i needed, as i wasn't in the truck for him to check.... got home, took old belt off, and checked them against each other only to find that the one i removed was longer, well, i looked at the alt pulley and thought, there can't possibly be one smaller than that, so it should be the short belt i need, which is the one the specialist gave me, so, i fitted it......... and lo and behold, the truck now runs so much quiter its almost unreal....... i guess there wasn't quite enough tension on the various pulleys with the longer belt fitted......
So, check what belt you have, and what pulley you've got.............