problem at 3,500 RPM's

i just noticed it yesturday. i got on the freeway and everything was cool on 1st and 2nd gear but when i got on it on 3rd at 3,500 RPM's it felt like it wasnt gaining any more and i noticed that my valves sound louder. kind of like when a honda v-tech valve sound when it kicks in. its a 2000 GT Vert with 80k miles. this is my first and only pony so i dont know much about the engin (YET) but if the car has been ran hard no drag little street race mostly pushing hard on the street as a daily driver. would i have to get my valve train checked? i now it wouldnt hurt but is this something that will normaly happen? i use good oil on a regular basis. the only thing i have lagged on is spark plugs. i have denso iridiums but no time to put them on. last time i changed them was about 4 months ago and i used some autolights (not sure). maybe its just time to change them and im just over reacting. but i am concerned about the valves sounding they way they do. any ideas?

OH WOW didn’t now that’s what pinging or detonation sounded like. I heard dreadful stories about that. ever since the gas prices started to shooting up i went from 91 to 89 octane. but haven’t heard any of it till ended up next to a wall on the on ramp and heard that valve chatter. By that time i had been running 89 for a few months so I don’t have a clue if it went away with 91. ill fill up with 91 and see what it sounds like then. if it still continues what then?