Discovery 2 annoying squeak!

Hi all, sorry if this is posted in the wrong area. I'm new to the forum and it wouldn't let me post in the other areas. I'm new to Land Rover ownership, I've just had a new exhaust manifold on my td5 due to the manifold warping and snapping 2 studs and giving me a lovely squeal when accerlating. That's sorted now but I now have a squeak when driving only when accelerating lightly at around 1800-2500 revs. It's an auto and when under more load there's no squeak. Just when cruising, very annoying! I didn't have the squeak before the manifold was changed so I'm just wandering if it's something like the air con compressor as I'm pretty sure this would have to be removed to fit the new manifold. I've checked the new manifold and there's no leaks. I'm planning on taking it back to the garage that changed the manifold but it's going to be hard to diagnose as it only happens when I'm moving! I've also pulled the handbrake gently while squeeking to rule that out. Any ideas or experience of similar problems would be a massive help. Ideally I'd like to find it without taking it back to the garage as it'll probably cost me loads of new parts in trial and error! Cheers Russ