without hearing the noise I would still say check it. Disconnect it from engine. If noise stops you know.
After reading this statement " I can hear the noise after the peak RPM just as its coming down off of load" leads me to think one or more rod bearings. If the engine idles smooth and runs like it should, I doubt its cam or ignition related. Drop the pan and take a look at the rod bearings.
If your engine sounds like this, you might be hosed: I doubt it's a rod kock. Get a good clear video of the car making the noise. Could be as simple as a flexplate bolt coming loose. PS: RIP Buick 350. It's sitting in my garage now while I'm messing with my SP 350. It's saveable, just don't have time.
AHA! - happily it was just one of the new rocker retainers that came off at initial startup - put back together now and running excellent
Priced it out, anywhere from 1500-2000. It wasn't too bad, that rod is most likely junk, all the others would need checked and resized with new bolts if they're saveable. The crank definitely needs turned, if it needs it past .020 I'll probably just get another. It was my first engine build when I was 17 (two years ago), and my dumbass forgot the oil galley plugs on either side of the cam. I broke the engine in with no oil pressure (thought I had a bad gauge, had no money for a new one, again, was a dumb kid), noticed the problem and fixed it (engine only had about 45 minutes of run time, and maybe two miles on it before the rockers/lifters started tapping), and it ran great with 25psi hot at idle, 60psi at 5k, for 5500 miles. Then one day on my way to school, knockknockknockknockknockknock. I took it apart, the cheap ass cam bearing disintegrated (probably from no oil pressure), and sent the metal everywhere. All the bearings had scratches, but the crank was only bad to the eye on #7 rod journal. The #3 rod bearing set looked like the surface of mars, but the crank was oddly fine. It's repairable, just a tad disheartening. Engine looked great everywhere else though. Didn't use a drop of oil either. Ran really tight, was snappy great throttle response. I might build it the same way I did, but with a touch more compression. it only had like 7.8:1 with those hyper .030 pistons. Anyway, glad you got it running good and it was something simple. I'll end my rambling now lol.
