Whenever I accelerate, I can hear a faint, rapid ticking... It only happens when I'm moving, not parked, and I can only hear it when I drive by something solid like a wall so it's magnified... It's been suggested it's bad gas, but no matter where/what type of gas I get, it ticks. I'm thinking maybe the lifters? How bad/damaging is that, and how easy is it to fix? Any other ideas? I know my IAC valve is going bad/ bad, could that be it?