It can only by heard while when pedaling, but it's not there 100% of the time. It's like a clunk-clunk, louder when pushing stronger or going faster, usually more than 1 clunk per crankset rev.
Shifting has a high chance of triggering it, but it will also occasionally rear its ugly face when I resume pedalling after coasting. Often I can get of rid of it just by coasting and resuming again.
With the sole exception of the derailers, all of the transmission has been replaced 3 months ago or less, and that includes chain, crankset, and freewheel. FTR the chain is a SRAM PC-830 and the freewheel is a 7-speed DNP Epoch.
I checked play as per Sheldon Brown's instructions and there's more on the new FW than the old one. Tried tightening the thing with a chain tool but it won't budge. I can't remember whether I greased the thread before screwing it in (did the work on a hurry and could've forgot), although I can't see how that would make a difference in this case?
Does my suspicion sound correct and if so, is there anything I can do?