The 357 I just built has a tick/rattle that you can hear under load and I can't figure it out. The best way I can think to describe it is "diesel-like" in sound. At idle and past about 2500rpm you can't hear it. It's not spark knock, I've checked the knock sensor with a hammer and it works, and pulling timing didn't help. I thought maybe it was from the small weld pinhole in my fabbed exhaust (which is the only leak I could find) and fixed that last night with no change in sound. Oil pressure & level is good. 80psi cold and about 40 warm at idle according to the stock gauge. Could it be a lifter or something mechanical? The engine has less than 150 miles on it so far. I converted the engine to an OE-roller setup and adjusted the lash a half turn past the pushrod spinning by hand (same as I have done with my other SBC). It runs well, but just doesn't sound normal.