Hey Everyone,
Apologies for the lack of reply, life has been a bit crazy and also forum notifications don't seem to be working properly. I still can't seem to get to the bottom of the noise, but thanks to everyone for their advice. Troubleshooting has been a bit of a saga, so here are the updates:
A few days after my last reply I started noticing some misfires, long story short, bad plug wires. With new plug wires in, it still wasn't running right so I pulled the valve covers and Cylinder 4's exhaust pushrod was a bit off center, when I loosened the adjustment nut, it fell straight in. Thankfully I was able to fish it out with a magnet on a stick and it wasn't bent. Turns out the bolt to secure the spark plug wire holder was too long and was interfering with the pushrod. Bolt removed, pushrod re-installed, readjusted valve lash on Cylinder 4 for good measure and fired the engine up.
Still not running great, pulled all the plugs and they were pretty fouled up so cleaned them up and voila, engine now runs great. That said, the noise is still there, though not as prevalent. This is the most recent video I just took. When the engine is fully warmed up, the noise can be heard with the hood close as it idles in my driveway. It sounds like it coming from around the oil pan area when under the car, and around the back of the engine when around the sides. When in front of the car it sounds like the water pump. Guess it's one of those cases of the sound bouncing around.
https://www.youtube.com/watch?v=dZJ1PDEbUJ8
If you notice in the video too, it almost seems like it's got a small miss. I know these engines don't idle perfectly smooth, and you can barely notice it, maybe I'm just being paranoid. My big concern is worn bearings. If you guys have a second, let me know what you think, and as always, thanks again!
Vince