Hello everyone, unfortunately my first post is a unpleasant one but hopefully you guys can help me out.

Yesterday I traded my Ranger for a 2000 Rodeo LS 3.2 w/ auto trans and 149,600 miles. I test drove it and it was super smooth, runs great, shifts great and a very sharp truck with no rust (from what I hear that is a feat on it's own). I have driven it over 100 miles since yesterday and all has seemed well until this evening. While I was sitting in the drive way in park and was reaching behind the seat to get something I accidentally blipped the throttle with my foot and heard a horrible noise that sounds like a rod knocking. I shut off the truck, popped the hood and checked the oil ( full and clean just like it was when I traded for it). Restarted the truck and revved it again to which the knock starts at 2,500 RPM and stops at 4,000. This only happens in neutral at 2,500 to 4,00 and never before 2,500 rpms or when in any gear driving.

Being that I just got this truck I do not know it's service history or past but the truck looks super sharp and doesn't show signs of abuse. I checked all heat shields that I could find and don't see a thing loose. I also hoped it was the timing belt tensioner but I heard it starts knocking at idle and stops at 2,500 rpm. I am at loss right now and disappointed because this is one of the nicest trucks I have owned. Any thoughts on what to check or should I drive it till a rod comes through the side?

 

Little extra info, I read to test for a rod you can disconnect a plug and the knock will go away if it's on that cylinder, well when I disconnected plugs 2-6 nothing changed and the knock still existed at 2,500, when I disconnected plug 1 the engine got a light knock at idle then when I reconnected plug 1 the engine ran smooth again?? So instead of the knock going away it actually started a light knock at idle then cleared back up when the plug was reconnected? I'm confused as to what this means.