New fatbikes have a ProWheel MPX 11 crankset 1x (hollowtech ii compatible set) and I get moderate clicking from mine, oddly, to my mind, not just when under power, but with less vigorous spindle spinnning.
I'm pretty familiar with hollowtech cranks by Shimano and getting preload set for the exterior cup bearings using that plastic cap on the left side. I've never heard a peep from these, and we have 2-4 in the stable. I have no good way to measure the actual torque on those shimanos given it takes an odd little can-opener type key. But again, never a peep.
Fatbike spindle/bb seems to give these clicks, but no feeling of play. Pulled the crank and checked tightness on the exterior-bearing bb, those seemed nice and tight. Put the cranks back on, tightened that plastic cap to about what I felt on the shimano (like 2 NM?), and locked the crank arm down well with the 2 M6 screws that hold it on the spline. Still, I get the clicking. Only when riding, though. Can't duplicate with complete zero pressure on bike stand.
Also checked pedals, they're tight.
Too little preload on the sides of those cartridge bearings? Too much? Another suspect to check?
EDIT: Still working through this, decided to try standing up to pedal for a good while, and no noise while standing, still or pedaling. I immediately checked seat post clamp and seat rail bolt, and both were pretty tight, but took another 1/10th turn or so each. Noise was still there.
But, this morning, which looking bike over for other potential issues, and wondering if maybe the seat itself were bad (cracked?) I noticed that the barrel-shaped nut that tightens the seat down in angle and to the rails was crooked, off by like 30 degrees. So, instead of a nice tight splined clamping force across a couple cm^2, I had a couple of cockeyed point loads. I remedied that, and I suspect that will be the real fix. Testing today.
EDIT: Testing shows it wasn't the poorly-clamped seat causing the noise, as the slight clicks are still there, though again, not on standing, and persists with very light pedaling, making me think it's likely not crank / pedal / spindle.