What causes the chirping on acceleration of my Land Rover?

When I accelerate, I get a chirping noise. Usually only during light acceleration - if I hit it hard, it doesn't seem to do it. As soon as I pull my foot off the accelerator, it goes away. I just had a serpentine belt replaced and that didn't make it go away. Mechanic is now saying it's a bad U-joint but that doesn't likely as it's not a clunking - it's a definite chirping (high pitched) HELP?|||Sure sounds like a belt. Check the belt tensioner, they have a bearing in them and if the bearing is going out it could be seizing and causing the problem|||have the tensioner checked on the serpentine belt, sounds like it's not keeping the belt completely tight.