I should have clarified, the noise happens when I insert the key, not when I start the engine (although it does continue when I start it up). And I left the key in and got under the car, it sounded like it was coming from what I believe to be the pump (under the gas tank, axle side) which appears to be an aftermarket Holley pump. If that's not the pump and i'm completely wrong...uh...lol? Either way, whatever that thing is, it's making a noise that worries me. I'll try to get a pic of the offending part when I get home later.
Thank you for your reply, very informative!