Engine Tapping Noise

[tjcbenz]

I have an 05 5.3 and I've had it for about 3 weeks now. I have not noticed any noises out of it during these last 3 weeks. I've done quite a bit of searching on here regarding noises and of course the subject of piston slap comes up. I've never heard anything like described, cold or hot. And also from what I gather, they had the problem fixed by 05. Yesterday I changed my oil with Mobil1 5W-30 "Truck and SUV formula" (what the differnece is, I don't know). Today I washed the truck and then after I dried it, I took it out for a 10-15 minute spin, after I got back I pulled back into the driveway and let it idle while I was going around it to get any stray water that had come out during my spin. Then...while I was bending over by the front wheelwell...I heard a tapping noise. Not extremely loud, but definitely audible. I stuck my head under the truck and did the "long screw driver stethoscope" method on the pan and the side of the block. Just listening there and holding my other ear, I could not hear anything through my "stethoscope". But just regular listening to it, there it was. I opened the hood, and I couldn't really hear it under the hood. Checked the heads for noises and all I heard was normal valvetrain noise, nothing unusual. Now I never actually looked for noises before, so I can't say if it was there or not before the oil change. I don't see how Mobil1 is going to make it make noise and whatever bulk-oil junk the car lot put in it didn't make it make noise. Motor has 70k and looks extremely clean inside when I took off the oil filler neck to check. No varnish/sludge visible. Long post I know, but I want to give the most detailed account that I can. Thanks for any info.