I cannot really explain you what it sounds like, But a simple explanation is the valve is staying somewhat open under high RPM because the springs are too soft to keep it closed. Im sure you will hear abnormal valve train noises and you will know when they float. If you ae paying attention to the tach dont go above that RPM until you shim your stock springs or stiffer springs.

I CALLED MB AND ASKED THEM IF THAT WAS NORMAL FOR IT TO SPIN UP THAT HIGH, HE TOLD ME THAT EVERY MOTOR IS DIFFERENT AND I JUST GOT A GOOD ONE. HE SAID HE WOULD NOT RUN IT OVER 4230 BECAUSE THE VALVES MAY START TO FLOAT.HE SAID IT WILL NOT HURT MY MOTOR IN NO WAY. I HAVE TURNED UP 4350 BEFORE BUT I HAD TO TURN MY SCREEW IN A LITTLE AND BELIEVE IT OR NOT I STILL WAS NOT BUMPING THE REV LIMITER IT MUST BE BROKE AND MY MOTOR IS BRAND NEW