I imagine you were legering since you mentioned being in the dark.
The grating you hear is bits of grit etc trapped behind the spool. The grit is often out of the water your fishing in and stuck to your line when you wind in. The rain then drips behind your reel and takes the grit with it. To stop that you only need to remove the spool and wipe round the spool and backplate to remove the moisture and grit at the same time.
No idea why the pawl slipped round
.
I mostly trott a float with my centrepins and manys the time i've been stood mid river and the heavens have opened. The water can pool up at the bottom of the reel between the spool and backplate. This stops the reel from running as freely so every now and then it may be necessary to remove the spool, give the reel a quick shake and allow the water to run out, or better still, give the spool and backplate a quick wipe clean. As soon as you replace the spool it wil run freely once more.
Another PITA caused by rain when using your centrepin reel is when you hook a decent sized fish and your playing it usiing your thumb, or other digit. The water can cause the spool rim to catch/stick on your skin, so causes you to have a sticky drag as you had with the old abu 506' s etc.
A knerled rim works better in those situations, although I always manage ok.