Knock sound

[DCMetroRacing]

Pulling into Wendys at lunch I heard what sounded like a knocking sound. Lower pitch then a valve tap, coming from the lower part of the engine. I'm going to get under it later today to make sure its not coming from the transmission and get some audio. Its hard to describe the sound and only seems to happen when the car is sitting still. When I rev it doesn't go faster. Any idea's on what to look at or what it could be?

[Aries]

possibly a loose bold on the oil pan, but more than likely a rod knock. (Yes, I know that's not what you wanted to hear...)

Hope it's from the transmission.transmission problems are easier to diagnose.

[DCMetroRacing]

If a rod knock, how long do you think the engine has left before it dies?