I'm working on a project and I purchased this rebuilt Buick 231 3.8L V-6 engine 3 years and 11 months ago by a reputable engine rebuilding company. The engine has been sitting in the crate that it came in for most of the 3 years and 11 months and I recently installed it in my project car. Today I finally started it up. After turning the engine over for a few cranks to pick the engine oil pressure, I then hooked up the ignition wire to see if the engine would start up. It did. I have two oil pressure gauges hooked up, one mechanical and one electrical. They both had the same reading when the engine started. If I remember correctly that reading was around 50 psi. The engine starts up on a dime and runs smooth. However, there is a loud noise coming from the engine oil pan area. Sounds like some type of an engine knock. Any suggestions as to identifying what type of knock that may be? Thanks for your support.