Engine ticking

My car has a ticking sound coming from the motor. It sounds like top of motor near firewall. The sound only can be heard after the car has warmed up and the ticking gets louder and faster with higher rpm's. It does not sound like a rod knocking as that would start knocking right away. There is no metal shavings in oil or transmission fluid and it only has 114,000 miles. It does not seem to affect the performance but sounds terrible when I accelerate and a bit embarrassing sitting in traffic. I am afraid it is (or will be) a major problem. Please help