noisy belt

wondering if any one could help me with aproblem on a 98 freelander 2.0 diesel its got a noise coming from the serpentine belt like a bit of clicking and a growling sound .when sprayed with wd 40 the noise disapears then its back 5 min later .is there a common fault on these in this area the vehicle as been standing for about a month and also it is fitted with air con . any idea of costs or supply of parts would be much welcomed regards mick

Had a similar growling sound from a RAV4 once & it turned out to be a rough bearing, can't remember if it was an idler or tensioner, but do a belt change & renew any tensioners etc. You'll have to wait for the serious experts to reply for a costing & other potential causes.