Car making ticking noise out of nowhere?

I have a 1991 Ford Ranger and I've never had a problem with it. Right after an oil change a few days ago it started making a ticking noise. I've had some people tell me it could be an exhaust leak and I've had some people tell me it could be lifters tapping (god I hope not). The sound can only be heard when in park. For some reason even when I'm idling in Drive I can't hear it at all. When in park it's loud. Also, It's much louder from underneath the truck towards the front close to where the exhaust manifold comes out and connects with the pipe. Can anyone give me some ideas or tips on how to diagnose this issue? Aslo, what are the differences in exhaust leak noises and lifter noises. I've heard it could be the oil pump too but idk.

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