Engine is making a strange sound.

I just finished the process of moving my entire setup to a Giant mountain bike that uses a lighter, stronger frame than what I was previously using. My chain tension is great, my engine is mounted level, my spark plug is a nice chocolatey tan colour, I blew through my muffler and it's free flowing, and everything works great. I also changed the head gasket and properly torqued it down evenly. My compression in my engine is excellent. Also, my c clip in my carburetor is set to the standard 2nd notch from the top which has worked well for me.

However on one of my test rides today, at around mid-high throttle, I'm hearing this very strange like, hallowed sound. Maybe like a bogging sound? I'm not quite sure. I've never heard my engine make this noise, and it has several hundred miles on it.

Perhaps tomorrow I will record a 480p video of a test run that will capture how it sounds and post it here for further information.

My bike isn't shaking or anything weird, and actually the sound sort of goes away when I go WOT. But I just know it isn't a healthy sound that shouldn't be there, and I'm just curious if this will eventually lead to my engine failing for some reason, if this is something that has happened to someone else.

Also just so you know, I'm only posting this thread because my horoscope today told me to, basically.

Although you may be feeling quite upbeat about your present circumstances, it's possible that you are fooling yourself. Naturally, it's useful to see both sides of an issue, yet your current tendency is to gloss over anything that may prove to be difficult. Unfortunately, denial will only act as a magnet, pulling in the very thing you are trying to avoid. Keep in mind that you don't need to embrace the shadows, but talking about your fears is the best way to dissipate them.

aaaaaaaaaaaaaaaaaaa

It doesn't sound like it's four stroking, it just sounds like, louder at mid-rpm. I need to get the camera from my girlfriend, but she's at work right now.

I don't see any reason why it would four stroke. In the process of moving the engine over I cleaned the air cleaner and made sure my carburetor was working. I'll post the video when she gets back.

Also just incase I didn't mention this already, my engine has a perfectly healthy idle. Something that is not usually associated with an engine that four strokes.

I figured out what was wrong, and it actually wasn't even my engine. One of the studs coming from my gas tank snapped, and my gas tank was vibrating on the frame. It totally sounded like it was coming from the engine. I'm glad it was the cheap $20 tank and not something mechanical. Lol.