I have a problem with my 1998 Grand Prix GT. There is a clacking noise coming from my engine that started happening during a long trip across west Texas (hot, 80mph, loaded down car). When it started, the check engine light came on a started blinking (cylinder misfire), although that went away. The noise is definitely coming from inside the engine, in the back by the firewall, but it's hard to pin down which side (if I stand on the right, it sounds like it's coming from the left and if I stand on the left, it sounds like it's coming from the right).
I thought it might be something in the valve train, since it sounded like it was coming from that area in the engine. So, I dug down in the engine, replaced the lifters, and removed the valves from the cylinder head. All the push rods, rockers, springs, and valves looked fine to me. When I put everything back together (replacing appropriate gaskets), the noise had not changed. I'm at a loss as to what's wrong. Any ideas?
Here is a video of what is going on taken after replacing the lifters. I took off the valve cover, hoping to see something useful. Sorry about the smoke, some oil spattered on the exhaust when I reved the engine.
Pontiac Grand Prix Noise - YouTube
Thank you!