Be aware that on 2002 and later 996/7's that display misfire codes, smoke, and have high oil consumption, the symptoms might indicate that the pistons are seizing in their bores.

I have seen a few with these symptoms; and after performing a compression and leakdown test , I found that the compression was lower on the cylinders that coded the most frequently. The leakdowns were additionally in the 20 to 30 percent range.on the suspect cylinders. I then borescoped the cylinders. Here are some photos of the damage:

Note the crack in the second and third picture.

Here is an 04 4s with 65k. Both rear O2's were starting to fluctuate . the roughness factor was higher on the left side. This is #2 cylinder.

It seems that one common symptom is a tapping sound that originates at idle during the cold start. It then increases in magnitude will occur when the engine is fully warmed. Noticeable oil smoke will be emitted through the cats.