Engine Noise

I have a 1999 Range Rover 2.5DSE diesel automatic. When pulling away from stationery or accelerating up a hill the engine makes a louder noise than usual and appears to be struggling a little.
Once on the level the engine noise quietens down once the car has gone through the gears.
It has covered 130,000 miles and is used daily.
Does anyone have this problem or can guide me as to what is wrong and if its worth getting repaired?
Thanks

if you reckon it g/box related you could start by checking the g/box fluid!!!

Excuse my ignorance. How do I do that and what type of oil should I use?

is there a yellow filler cap near bulhead? kinda like oil dipsick but obviously not the oil dipstick. i have a 96 petrol and thats what mine has for transmission fluid. i'm not sure about the diesel tho. on some(later petrol models) i think you have to get underneath. do you have rave cd

cd 2 is what you need its the workshop manual and can tell you quite alot of stuff!