I have a ticking noise coming from under the hood of my '91 DeVille, it's inaudible when the hood is closed, but once you open it you can hear it fairly well. I think it's the exhaust because it seems to be coming from the pipe as it sounds like it reverberates throughout the whole pipe, but it could be coming from the heads, but there is a scent of exhaust sometimes.

Does anyone know of any way to tell precisely what it is without taking it to a shop? Also, it isn't throwing any codes.

Edit: I forgot to mention that it's the stock 14 year old exhaust, and it was driven in Ohio in the winter for 4-5 years.

Take a piece of garden hose and direct one end to where you think the noise is coming from, the other end to your good ear. Move it around till you find the source.