2004 Chevy Camaro Z28 my engine makes a horrible ticking/clattering noise

2004 Chevy Camaro Z28 mileage 34,500: Four times now I have taken my car in for service at two Chevy dealerships. Upon acceleration in any gear, either from a stop or on the road, my engine makes a horrible ticking/clattering noise. It seems worse when the car is warm or in warmer weather. My boyfriend has driven it claiming to hear it even when it's cold. The first visit to GM resulted in "That noise is normal for the Camaro. No one knows what it is." Second visit: "We have no idea." The third visit seemed a little more revolutionary: "It’s fuel clatter you need to use premium fuel and the problem will resolve." For the next 10 months I resolved to use only 89 or higher fuel (previously I had used alternating tanks of 87 and 92). Well, the noise grew worse. I just picked up my car from the FOURTH visit and got conflicting advice. First I was told "You probably shouldn't use high grade fuel since I don't believe this car requires it." And then from a DIFFERENT tech, "There is nothing we can do about it; you can only use premium 91-grade fuel." Now I am frustrated and worried since my manual claims this noise/problem can be harmful to my engine if not serviced. I am still under warranty is it something that can be remedied?