TD5 air compressor

I notice lately after stopping and switching off the engine, as I am getting out, there appears to be a loud 'farting' noise coming from the nearside of the Disco in the region of the air compressor, is something packing up.

Assuming it's just a quick burst of air then it is just the self levelling suspension lowering a bit, which it normally does when people get out.

It has only just started doing this, which is worrying as obviously something has changed / deteriated. Of course there has been a lot of huge puddles around my area which I have delighted in ploughing through without slowing down and I am thinking perhaps water has drenched the compressor and associated kit and causing this problem. Another job for the weekend.