2011 5.3 making a ticking noise

[Amphere1999]

I was driving home from out of town last night on a 200 mile trip.  About 40 miles into the trip I stopped for gas.  After getting back on the freeway my CEL came on.  I happened to have my OBII reader plugged in so I grabbed the code and it was a P0521.  I replaced the oil pressure sensor a year ago when this same code came up.  A little while later into the trip the truck started making a ticking noise.  It became more frequent as engine rpms increased.  The oil pressure gauge read normal as well as the temp.  I stopped and checked the oil and it wasn't low.  I was limited to the troubleshooting I could do at night in a gas station so I continued on with the trip and made it home without incident.  I didn't notice any loss of power or any other difference in the way it ran.  This morning I got in it to go to work and the ticking noise was gone although the CEL was still on (I haven't bothered clearing it with the OBII reader yet).  I thought maybe it was a lifter tapping although it didn't quite sound like that.  It is really strange that the ticking was gone this morning.  Any suggestions as to what may be causing this?  It will be difficult to troubleshoot with it not currently making the noise.