nozomiyume

Alright, I'm not sure if anyone can offer any diagnosis since it's pretty tough to figure these things out without seeing the car in person... but I've recently started to have a pretty bad groan from the engine at pretty low rpms, right around 1.4-1.6k. It's bad enough that the gearshift vibrates in my hand. It's a 2000 V6 Firebird, and it's never done this before, about 49k miles on it.

Has anyone seen something like this before or have any suggestions? The oil was just changed pretty recently, and I'm almost 100% sure it's the engine, because it happens when I'm in neutral and not moving as well. I'm thinking about changing out the oil again, but I'm really not sure what caused it. Anyone have any suggestions on places to look / get started troubleshooting it?