Lexie's LS

I don't know if this is noteworthy or not, but it seems in the morning on a cold crank, I hear a low engine rumble the first 15 minutes of driving. Then there's nothing for the rest of the day--cold start or no--until the next day's cold start. That is to say, for the remainder of the same day, the engine runs very smooth and quiet. Standing next to the engine on the outside, you can hardly hear it.

Anyone notice similar symptoms? (engine or hearing...either one. Yeah...I'm that old!)