Strange rattle from engine - Perplexed.

[Humbucker]

Kinda long...

For those who have been following my AFR 185 head and Victor Jr intake install. Here's a brief refresher:

When the heads were first installed, we bent a pushrod on #6 intake. After much testing (thanks everyone, especially RT), it was determined by my friend and me to be a faulty pushrod. We installed upgraded pushrods, and to be safe, only went 1/4 turn from zero lash.

The next issue we ran into was a bad running engine. Very bad. After much testing, we found two sets of timing marks, and retimed with great success. It ran like a scalded dog. Only minor tuning issues from here. It did, however, make a funky rattling noise at about 2000-2100 RPM. It then went away until about 2700 RPM. It then rattled from 2700 RPM till about 3000. After that, I *think* it went away, but it was hard to tell with the side pipes blasting away.

I decided I'd go through the valve train and put another 1/8th turn. No help. I went another 1/4 (for a total of 5/8th turn). The rpm dependant rattle sound was still there.

At this point, I felt it *could* be an exhaust leak. I pulled the cheap Mr Gasket header gaskets that we used in lieu of Copper RTV and good felpro gaskets. No difference. Everything still the same.

I even drained the tank and put in 100 octane fuel to see if it was pinging I was hearing. Nothing changed.

I called a local performance shop and they feel it's either a jetting or a timing curve issue. I'm going there on Thursday morning and they're going to look everything over. After finding the problem, we're going to put it on the dyno and get the jetting and air fuel mixtures right. They are about 30 miles away, so I asked them what I should do about driving the car to them. They suggested I back the timing down by 2 degrees (it was then at 14 initial and 32 total). I did that last night. No difference.

I've tried to tighten everything I could get a wrench on. I'm at a loss. Anyone care to take a guess as to what's causing this mystery rattle? I'm assuming we'll find out on Thursday, but many of you are pros at this. What say you??

Jake "Sincerely Puzzled" Langston