Contrary to what some of the opinions may be from other posters here, a restricted heater core could cause such a noise. As the flow is restricted and air that may be in the system (that causes the restriction - gumming) is forced into the heater core, it can make a whistle/high pitch under hard RPM's. Its possible, but given that you just had a tuneup, the PCV valve was likely changed. Make sure the vent hose going to the PCV valve is tight as well as the PCV itself in the rocker and make sure the hose going from the throttle body to the other side is also secure. The rubber elbow that goes to the plastic cap on top of the throttle body may have become loose if they did a throttle body cleaning. Secure it tightly with a tie strap.