Any guesses about the diagnosis?

I have a 99 Plymouth Voyager with 125K miles. Last time I drove it, once the engine got fully warmed up, every time I came to a stop, with the engine idling, the oil light and audible warning came on. If I shifted to neutral and gave a bit of gas the warning went away. I am hoping that this is just a loose belt or something like that. However, I am quite ignorant of such things. Any guesses?