I think I might have an engine problem... :(

It sounds to me like all eight are making the noise......sounds like a diesel. This is usually a few things. First, it could be perfectly normal if it has floating wrist pins. They are known to make a little noise sometimes. Secondly, if it goes away or lessens significantly when warmed up, that's indicative of normal forged piston expansion......if so equipped. So it's possible the noise is normal. I have heard lots of engines do it, including some I have built myself.