Scary sounding question...

Ok, lately in the am, when I start my DII, I'm hearing a bottom end knock, only for about 2-3 sec's. I've only got 50k on the engine and it only does it when it's cold...like that will happen in AZ in the summer but, if it sits for some hours, it does it. Also, the oh so cordial "service engine soon" light comes on intermittently. It seems as though when I adjust the gas cap, eventually the light will go off so I'm assuming it's a vapor/return/or even worse, something emission related so, anyway, anyone ever heard if the oil pump is weak or...The good thing is I bought an extended warranty so, also, had it cover "everything", so I'll only be out 200.00 if it's something major, I'll repost after I get it back from the LR dealer...