If you’ve got a Fusion One kind (especially the Fusion Zero) then it’s extra important to keep that bolt tight as you’ve just got the one holding things together, and in the case of the Fusion Zero it’s well known for snapping if a little loose.
I found the clicking in the end, and it was the cranks I fitted recently. I don’t think they go on far enough as when I used the crank extraction tool using just finger power of turning the extractor was enough to pop off the crank. I can also so (i think) where there is slight wear where the crank has been moving ever so slightly.
If they are ISIS cranks you may be able to use a thinner spacer washer to tighten the cranks. Spacer washers of different thicknesses are available from UDC.
The standard instruction for determining the required spacer thickness is to push the crank on by hand and then select a spacer about 3 to 5mm less then the space from the bearing to the crank. With the correct spacer the crank will fit tight on the tapered ISIS spline and against the bearing when the attaching crank bolt is tightened.
This depends upon your crank material. For most aluminum alloys we have found a pre-load of 3-5mm is ideal (as measured according to drawing sheet three). The individual crankset manufacturer will have to determine their required pre-load for themselves, based on analysis and testing.