engine doesn't like to be tilted...
 

Why is it that after jacking up the back end of my car or being parked on a significant incline... There is a significant "knock" when starting the car shortly after. It's on the left bank... 1,2,3...Once the motor runs a bit it's fine... Doesn't matter if cold or hot nor is it everytime...

Any ideas?

That could actually be a problem -- my car doesn't do that. Additionally, I would think that steep downhills or even hard braking (I know, hard braking never occurs in these cars, but we must be prepared for all unlikely scenarios) would cause the same problem. Any more details on the problem?

Dan

Could it be that oil is getting past the rings and causing partial hydraulic lock? Either that or fuel, either way my car doesn't do that and it does not sound good at all.
Do you run your oil level at the upper range on the dip stick?

MY car puffs a little smoke on startup if I park it on an angle and leave it for a few hours.. However it only burns a quart every 800 miles or so

A "significant knock" is not good and not normal for a 911 that has been parked on any incline, no matter how steep. You should investigate further.

Are you sure it's not your parking brake braking loose. That also makes popping clinking kinda noise. Just something else to consider.

It could be fuel. It hic-uped slightly at startup when I turned the key, and I gave it a little throttle tap, then the noise started and in fact sounded like a knock. The more I think about the particular noise, it's not the same one I had heard before. This was much more distinct. It isn't doing it now... nor has it done it before.

I run my oil perfectly in the center of the stick or slightly lower, and this engine goes about 1200-1500 miles before needing a quart... (I'm REALLY lucky...)