01 4.7, 170k miles. Today, sitting at a stop light for about 10-20 seconds, hear a ding. Check gagues light was on, oil pressure gauge reading on the "L" line. As soon as I put it in neutral, it popped back up to the first line on the gague. It's done it to me a few times. It was a little low on oil, OK two quarts! even after filling it back up, it's still doing it. The engine makes no funny noises, even when the gague is sitting at the L. Any ideas? Thanks!