Piston clearances don't magically fix themselves every once in a while. If you have slap, you'll have it every time the engine runs under the same conditions.
Typical for it to lessen or disappear once the engine warms up. It's pretty harmless as long as you are reasonable with the motor until it comes up to temp.

 

Thank you all for your help. It is indeed coming from the flexplate, now it's just a matter of me getting under there and fixing it. So glad that even if the flexplate is cracked and I need to purchase a new one ($45 on partsgeek.com), at least I wont have to worry about replacing a piston, or anything in the top end. Thank you all for your help! I will post an after video once I get 'er fixed.

 

Cracked or just loose bolts?

 

Not sure yet, haven't gotten around to taking off the cover (the lack of tools in my house is disturbing), but 95% positive it is the flexplate causing the noise

 

I'm about 99% sure it's just the bolts. LOL.

 

does yours knock when first started? or only after its warmed up to operating temp? mine knocks onlyvwhen warm and knocks louder when the a/c is on? anybody?

 

Like i said before, it always knocks, on start-up, at operating temp, while driving, etc.

 

Well guys, unfortunately, it's not the bolts. I got down to business today, took off the flexplate cover, and to my horror, all the bolts were in tight, no slack in any of them. I am sure that the knocking is coming from the transmission, towards the flexplate, but it is not the bolts causing the problem.. ANY help at this point would be very helpful, otherwise it'll be time to call a mechanic.

 

Could be a cracked flex plate. They tend to crack around the crank bolts.

 

How about this?

Straightshooterjeeps cracked flexplate diagnosis
I removed 3 of the 4 bolts.

Then loosened the last bolt about half way.... I left this one in to maintain connection between the tq and the plate. Just so I wouln't have to fiddle with putting bolts back in too much.

Now the flexplate is pretty much seperate from the torque converter.

Got my flashlight pointed up in there

Grabbed a big flathead screwdriver and started prying on the flexplate

Don't see anything yet

Turn the flexplate a half rotation

Pry again

and there it is! A big fat crack up near the center of the plate.

When the flexplate is loose from the torque converter you can get it to "flex" real good and you just might be able to spot your crack.

Just to be sure you do have one before dissasembly.

It was very obvious at this point, but before pulling those bolts I looked and looked and could never see a crack.

Hope this helps save someone a little time.