small leak of red/pink oil on my x type 2.5 4 wheel perm drive 2001 reg?

x type 4 wheel perminant drive 51 plate 2.5 petrol the car has a low wering noise at 33 to 38 m p h ,now there is a small leak of transmition oil on my path i thiis the oil from the transfer 4 wheel drive box the car runs very well but for this noise which goes away at about 38 mph.it has only done 45,000mile