The temperature here was 37F this morning, overnight it dipped down into the 20's. When I started it up it knocked for about 7 seconds. I am running Mobil 1 High Mileage 5w30 with a Fram Ultra, a very stout combo so I dont think it would be oil, or filter related. This is the coldest morning we have had this year, so I dont think its a coincidence. Basically it had a knocking noise right after start up. I have never heard this before, it did quiet down but was still barely noticeable as I drove down the street then it went away all together after about a minute. I put in in drive and gave it a very small rev to see if it would present itself but no noise. No noise while driving around town this morning either. What part could cause this? I doubt its piston slap since its never made this noise before, and the noise went away in less than 10 seconds.