SBC Rocker arm tick

[53lowdown]

Ok, I'm stumped. I can't get a rocker arm to stop ticking. 1970, 350 chevy engine. Stock cam, hydraulic lifters. Engine was rebuilt I believe about 12 years ago, but has sat for years at a time since then. Oil pressure is normal. I've been using as daily driver for past couple of months, and this ticking I just can't figure out.

Issue: Exhaust rocker on #7 cylinder ticks nearly constantly. Not when first starting, but maybe a minute or two after startup, then almost all of the time. Sometimes at around 1600 RPM it will rhythmically tick for 5 seconds, stop ticking for 5 seconds, and repeat. I've used a hose as a stethoscope - It's not exhaust leak. The ticking is definately coming from the #7 exhaust rocker.

I've adjusted using standard methods, engine off, tdc #1, then tdc#6 per http://berlinetta.info/Lash.htm

Then also with engine running, loosen until clack, then tighten down until ticking stops, then 1/2 turn more.

In fact, it will continue to tick even when tightened so far that cylinder starts missing.

Looked at and measured the stud - it is not pulling out. Checked for weak/broken valve spring by pressing with hammer handle. It compresses same as other valves. Looked at rocker, washer and nut. all look good, but swapped the rocker, nut, washer and pushrod with another cylinder. Still no luck.

Ok, so it has to be a bad lifter right? Nope, just put in all new lifters, adjusted rockers using both methods and Exhaust #7 is still ticking. Can't adjust it away.

I followed this thread with a lot of interest because I'm having similar issues:
http://67-72chevytrucks.com/vboard/s...d.php?t=733510

Any other ideas? I'm thinking about just getting earmuffs....