If there was plenty of oil there after 10mins I wouldnt worry about it being low the first time.
There are usually only two things that make a tapping/knocking noise and thats the cam/lifters or the big ends... if it's the big ends then most of the time your oil pressure light will be on at idle (but not always), and for it to be the cam/lifters they either have to be really really worn (because they are hydraulic they will self adjust so accomodate wear and not tap) or have no oil getting to them.
Checking the oil pick up is a good idea, were you cornering hard or anything at the time and do you have a RST baffled sump?