I used my mechanic's stethoscope (long screwdriver with long aluminum rod on the end) to listen for a tick I've been hearing. The injectors are pretty loud when i listened but that seems like it would be normal. I listened around the engine to try and find this tick but couldn't. I listened on the valve cover for a rocker, maybe a pulley, and even on the pushrod and lifter side... Got nothing. I then went to the drivers side and listened around. I could slightly here it on the header. I moved lower and could get the stethoscope on the welch plugs from underneath and that's were it was noticeably louder. I have no idea what is there that could be making the noise unless my manifold is cracked and its somehow resonating on the welch plugs. It's a very consistent and continuous tick which makes me think it's valvetrain and not something rotational. what else could it be? Some said the purge valve is ticking but it was louder from underneath. Others say it's spark knock but again its so consistent that it doesn't sound like detonation. I will add that it is very distinct when driving with the top on or off. Even more distinct than listening with the hood open. Thanks in advance. Any help would be greatly appreciated.