Hissing when steering wheel turned full to the right

HI,
Getting this weird hissing noise coming from somewhere around the steering wheel when i've got it on full lock to the right. Doesn't do it on left..
Anyone any ideas what that could be?
Im an absolute novice in car mechanics, hopefully its something simple!
Freelander 05 Petrol 1.8l
Mickey

I had this problem which I identified before I bought the car. I suspected the non return valve in the steering rack. This valve is within the rack itself. I got the price of a new rack subtracted from the car price. Changing the rack solved the problem. Power steering worked ok before but the hiss drove me mad and I was concerned about the power steering failing. Rack about £150. Labour probs about 4 hours. Did mine myself but quite a big job. Sorry it isn't easy fix. It sounds like the steering wheel is the loudspeaker!!

Thanks for the advice and swift reply! Would you know if this is one of those things that's best being seen to urgently, or could leaving it a bit end up with worse ramifications than having to do the same work?

Now you are asking ! I changed the rack because a) I didn't know the answer to your question and b) it is a critical part of a car. I assume the worst that would happen would be to loose the power steering but that may not be the case as the rack is at fault so DON'T quote me !!

My experience told me that it was steering related and therefore as important to repair as a brake fix!

If you can DIY it can be done, but I am fairly experienced and it was a bit of a tricky one, working through the wheel arch holes and then lining up the new rack and steering column. Be interested in a garage quote - my estimate is 4 hours labour. Rack can be purchased on Ebay new for fair price if your garage will fit supplied parts??

My DIY skills are stretch as far as being proud that I found the oil dipstick.. so a trip to the car doctor may be in order! I'll try not to turn right too much in the meantime haha I'll make sure to post what my quote was/ if garage are thinking same thing thanks bud!