Im not intimately familiar with powerspline, but
Noises generally come from the interfaces between parts.
Things to check:
pedals, assuming aluminum crank arms and steel pedal spindles, make sure that there is a bit of grease on the threads where the pedal goes into the crank arm.
pedals again, if they are build in parts, if there is anything to tighten, check them.
crank arms, make sure they are tight.
with ordinary crank arms, do not grease the interface between arm and BB spindle, the arms will draw on too far, and may swage open. grease the bolt that holds them on, make sure they are tight. If there are torque specs, follow them.
powerspline, check that the interface is clean, make sure whatever bolt secures them is as tight as it should be. careful, steel into aluminum can lead to the aluminum threads pulling out.
chain rings, make sure the ring(s) are seated to the arms properly, pull the bolts out, grease the threads, reassemble, make sure they are tight
bottom bracket, what is the frame made of? how are the crank bearings secured to the frame?
steel, traditional bb bearing cups threaded into frame, make sure they are properly tight. usually the right cup tightens to the frame and the left is adjustable. your noise is from the left, when all the way down, or nearly so. the noise could be the adjustable cup moving. i'd check this soon, if the cup is moving, you can distort the BB shell. ( I did it to the right side of an old bike of mine, had to retap the BB shell to italian ( it was french ) threads to get the cup to hold. ) If it is steel/steel, and you end up removing the cups, grease the threads when putting it back. otherwise, not sure. steel to aluminum gives rise to all manner of noise, something that keeps the corrosion at bay is recommended.
aluminum frame, sealed bearing,my daughter's bike is like this, I have not managed to remove the creaking noise yet.