Rear end howling after that last desert trip

I took my Wrangler out for a weekend in the dunes a couple of weeks ago, nothing too crazy, just some gentle exploring and a bit of dune bashing with some friends, but ever since then I've noticed this really annoying howling or whining noise coming from the rear of the vehicle that just wasn't there before. It's most noticeable when I'm cruising at steady speeds between 60 and 80 km/h, and it seems to change pitch slightly depending on whether I'm accelerating or coasting, which from what I've read online is a pretty classic sign of differential trouble. I had a quick look underneath and I couldn't see any obvious leaks or damage, but I did notice that the rear diff cover looks like it's taken a bit of a hit from a rock or something, nothing major but there's a small dent that might have shifted things around inside. I'm really hoping it's just a low fluid level or maybe a bearing that's starting to wear, rather than something more serious like damaged ring and pinion gears, because I've seen the prices on those and it's not pretty at all. One of the guys from my off-road club mentioned that if I'm looking for a specialist, this Jeep differential repair garage covers Musaffah Shabiya and apparently they actually rebuild diffs properly rather than just swapping in second-hand units that might have their own hidden issues. I'm thinking I should get this sorted sooner rather than later because I know if I leave it, the noise will just get worse and eventually something might seize up completely. Has anyone here had a similar howling noise after off-roading and can tell me what the issue ended up being for them? I'd love to know whether I'm looking at a simple fluid change or something that's going to empty my wallet.