rush of air & high pitched sigh from left hand side below glove box?

hi, my rover 25 is making a very odd sighing noise on impact, sudden brake or jilt but also sometimes just randomly it seems to be coming from below the glove box i assume in the engine i thought it may be a bush or the suspension but i have the good old "little knowledge syndrome" & am very curious as well as concerned (it sounds like the squeaky penguin on toy story, a rush or leak of screaching air!) really appreciate help pls! :D