On a traditional connecting rod reciprocating engine, the 2700-3000 rpm zone is a magical area where internal dynamic forces go thru a transition.
At low rpms, the engine internal forces make sense in term of what we've been taught. Starting at bottom dead center initiating the compression stroke, the piston rises, compressing the mixture, and the connecting rod is experiencing compression force, increasing all the way up to top dead center, and increasing more from the combustion pressure pushing on the piston, delivering this push force thru the connecting rod to the crankpin, all the way down to bottom dead center and the end of the power stroke.
At high rpms, the connecting rod experiences reversed forces. Starting at BDC of the compression stroke, the piston is starting at zero speed, and must be accelerated to its maximum speed, which occurs around 80° BTDC. This acceleration plus compression of the mixture puts a very large compression force on the connecting rod. However, after this point, the piston speed rapidly reduces, and its inertia (plus the wristpin) induces a tension force on the connecting rod. This inertial slowing-down force is greater than the force of gas compression, producing the tension force on the rod. After TDC, even with combustion pressures acting on the piston, the accelerative forces of the piston being pulled down by the connecting rod exceed the combustion pressures, and the connecting rod is still in tension, until the piston max speed at about 80° ATDC, where the piston begins to slow, and the connecting rod now experiences compression.
Now, at mid rpms, around 2700-3000 rpm, (what GM calls the 'detonation prone zone'), these competing forces, compression/combustion pressures versus piston/wristpin inertial forces, enter an interesting limbo state, where the rod can experience either compressive or tensive force, depending on throttle position and ignition timing.
Since the connecting rod angles to-and-fro relative to the cylinder wall, the slipper piston will experience scuffing forces either on the frontside or backside of the cylinder, depending on whether it's pushing down on the rod, or being pulled down by it.
So, there's three zones of force dynamics. Low rpm, predictive conrod compression. High rpm, predictive conrod tension. Mid rpm, the 'limbo' zone', where rattling of a worn engine can occur.
Experiencing a change of vibration while moving thru these rpm zones is normal, for a 360° vertical twin, but can be mitigated by being in a good state of tune, proper carb adjustment, and ignition timing.
However, rattling and knocking in this mid-zone is a sign of problems...