Engine Noise

[Matt]

Ok, let's see if you can diagnose an engine noise w/o hearing it....

Sometimes when I start my 94 SE-R up, (usually only when it's been turned off for at least half an hour), the engine makes a loud noise for a few seconds, and then it goes a way.  The best way to describe it, is that it sounds like a combination of a diesel engine and a vibration/grinding sound.  My Dad was thinking maybe one of the cylinders was missing and causing the engine to vibrate.  That doesn't really make sense to me because it only happens on startup, and not every time.  Anyone else experienced this?

Thanks,