Name That Noise, opinions needed Options

[goose2]

Ok flat six gurus...let's play Name That Noise. The motor is a 2.4 six, has the chain tensioner upgrade, unknown mileage but good compression, normal oil consumption, runs very strong (except for some Zenith carb issues), minimal oil leakage, non-smoker. Sounds good, yes? I think so too, but something's not right. The first clue is a valve noise that comes and goes very quickly...a loud click-click-click that stands out above all the other nice mechanical music this motor plays. Two very careful valve adjustments have made no difference. This occurs hot or cold, but slightly more often hot. The noise is there maybe 50% of the time and can come and go in a couple seconds time. If I had to guess it's point of origin, I'd say # 4 or 5 exhaust but that's a tough guess. I've now put over 1000 miles on the critter hoping it would go away but it's not. I've searched message boards, talked to local Porsche mechanics, read all the books. Opinions range from "don't worry about it, when it gets worse it'll be obvious where it's coming from"...to"you'd better do a top end job on it now before it self destructs" Suggetions include sticking valve, bad swivel foot adjuster, worn valve guide, oiling problem, sloppy rocker shaft, and cam end thrust problem.

Second clue, not necessarily related. A strange noise noticable at idle to around 2k rpm. It may be present above that speed but other noises drown it out. It's a sort of muffled deep ka-bunk-a bunk-dunk....not a tapping like a bearing, or a clicking like valve train, or a rattle like timing chain. My mechanical experience would suggest crank end play, loose flywheel or something like that, but it does not change with the clutch in as one would expect if that were the case. This noise does not seem closely correlated with engine speed like valves or bearings. It could even be something other than the engine rattling against the body but I've checked for contact anywhere like engine shroud, exhaust system, etc. Does the dry sump oil system make noise maybe? It's almost a liquid sound like gurgling. Could this be related somehow to my valve noise?

I hope my noise descriptions make some sense...I realize it's pretty hard to diagnose sounds by a verbal description over the internet. I'm just trying to narrow things down as much as possible before deciding what to do about it. I know we have an incredible amout of talent, skill, and experience among our members. All opinions welcome, Thanks.
Randy