Would seem you could lift off plug wires one at a time to isolate.

 

Here you go - see attachment.

 

For a second there, it sounded like a chipmunk on a drum set, speed up.....lol.

Normally, a bad lifter will be a a typical continual tapping sound. It is an intermediate knock, I too am leaning on the IACV freaking out...

BTW..What is the oil level like?

 

Wait a minute, we need to do some other work first.
Remove the belt and then run the engine.
If noise is still there put belt back on, unplug the IACV and then see if the noise continues.

 

Sounds pretty fast for a sticky lifter at idle, and if IACV was moving all over the place, wouldn't idle speed surge around as well? Could be belt driven, could be belt shredding, could be in valve train just under the valve cover. Like Spike says, more tests, less wrench. If you can listen with a stick or long screw driver, might point to which valve cover to open first.

 

I'm 90% positive it is not a valve train problem, valves move slower and make a slower rhythmic sound, tunk.....tunk.....tunk....
Even bad lifters dont make that fast of a noise at idle, it is a electrical problem, my money is on the IACV.

 

you guys are ****in geniuses, and maybe so am I cause thats all I could think about - it was way too fast for a stuck lifter at idle. so i went out in the rain and wind and took the belt off. NO NOISE!!! ha!

so neighbors peeking out their windows as I am cavorting around in the driveway in the pouring rain with my mad scientist headlamp on pretty much stopped me there (well, to be truthful it was the lovely Mrs. geek that stopped me)

so now I have to do two things - make it make the noise again with the belt on and then isolate the problem. everything spins pretty well, but the tensioner has a little wobble to it and the alternator feels, well, not really gravelly, but a bit lumpier than I would like as I turn it. Outer ac spins freely but the unclutchted part is very hard to turn by hand.

did i mention that you guys are ****in geniuses?

 

Listen to those things with a stick as well, you'll be surpised how well you can hear a bad bearing, etc. But you must have the lovely Mrs. geek's permission before use of the broom stick - don't want to wake up the flyin' monkeys! Would be a good time to check all fluids also (power steering...).

 

The alt you can place your hand on while running and feel the noise if that is the culprit.
Many years ago I thought I threw a rod on my Rover, it knocked so bad and loud I swore the lower end was gone.
Removed the belt, noise gone.
Spun the alt, lnocked.
Put belt back and placed my hand on the alt and it vibrated like a jack hammer, thunk thunk thunk, just that quick too, fast and loud.

 

One for you, one for me! I will get to it in the am and keep you posted!