[DRASTiK]

Lifters: Did you give the new lifters an "oil bath" before you installed them? The best thing to do is to submerge the lifter in oil and use an old pushrod to pump them up manually prior to installation. If not, then yes, it's possible that your lifter(s) just haven't pump up yet. On the other hand, if that was the case, then it would most likely be more of a rythmic ticking noise, not a sparratic (sp?) one. If the noise doesn't sound like it's breaking anything (see below), then just run it for about ten minutes or so at idle and see if it goes away.

Without hearing the noise, we can only guess at the cause. How loud is it on the loudest side? Is it REAL loud and teeth grinding, or is it more of just a tick that you can hear standing beside the car? If it's not rythmic, then it could be a plug wire isn't seated on the plug correctly and you're hearing it spark.

If you couldn't tell, the part that is confusing me is when you said "The sound does not have a steady rhythm." That statement tends to lead me away from the rockers/lifters. But hopefully that's all it is and nothing worse. As far as exhaust leaks, just start the car when it's cool, and before it has a chance to heat up, put your hands around where the headers bolt up to the heads, and around the flange. If air's coming out, you'll definately feel it. Hope this helps, keep us informed,
Dave