Strange sound...

hi everyone,
I did a quick search for this but couldn't find anything so sorry if it's repeated.
I have a td5 disco and as I'm driving there is a sound coming from the centre/gearbox area which sounds like bubbling/sloshing water or liquid of some kind.
Can't figure out what it is, iv checked the drains for the aircon, they were blocked so emptied them out and no difference. A couple of weeks ago i had the top hose and coolant replaced, at the same time I got him to check the transfer box and gearbox levels (whether he actually did or not I'll never know) but he said they were fine.
Normally I'd do all that myself but all my stuff is in storage at the minute so iv only got a small amount of tools.
Can't think of anything that it could be so any ideas would be very much appreciated!
Thanks

Give a good bleed to the cooling system then after a longer drive open again the bleed screw...if there will be bubbles again unfortunately it can be a combustion gas leak into the cooling system which means HG failure or cracked head, i've seen this 4 times and that gurgling from the matrix area was the symptom on all.... isn't that new top hose a bit hard when the engine is hot?

Thanks for your reply!
Hopefully it's not the Hg or the head, that wouldn't be ideal at all! Haha
I have tried what you suggested, gave it a bleed, topped it up, and have been driving it for a while, it wasn't hard driving, just around and about, the engines been running for nearly 2 hours and been up to temp for majority of the time. Got home and opened the bleed screw, nothing but liquid came out. Also the top hose wasn't hard as such, I could still squash it relatively easily.
Any more suggestions?!

Was the sound the same after the bleeding?

Yeah it was the same. Not sure if it makes a difference but it had a new/reconditioned gearbox a couple of years ago.
I'm wondering if there is anything in that area that could have somehow become full of water?!
Sorry for my lack of knowledge, never had a td5 until I bought this a couple of months ago, I'm used to the simple times of the 200tdi, haha