Is it more like a whine/groan or a whine/belt squeal? Either way I'd go ahead and check the fluid.

But if it's more of a whine/groan I would guess your pump is going out. If it's more of a whine/squeal I would guess the belt needs tightening or replacing.

All guesses/ideas, but hopefully it might start you in the right direction. :10q: ..Hopefully