Creaky sound coming from crank

I thought I had a creaky crank or pedal, after an expensive service didn't cure it google suggested it might be my cleats. It was! Moving them inboard all the way got rid of it.

Since you mentioned the lower half of the cassette -- it's possible that the cassette itself is creaking. I had a creaking sound that I thought was from the BB or crank, but it was only noticeable on the 3 largest cogs of the cassette. It went away after lightly greasing the part of the hub that touches the cassette, and tightening the cassette locking to the proper torque.

One of my bikes has been making a creaking noise in exactly the same part of the pedal stroke. Turned out to be the pedal bearings.

I also have a suspicion the freehub is shot, as it's still got another issue with noise under load.

I've had a creaky pedal thread in the past.

I used a more waterproof grease and Bang! the creak is gone...

I had gotten a thread-together adapter for my CAAD8 (BB30), but after a while the creaks came back.  I did some tests to try to isolate the bottom bracket (i.e. had wheels off the ground and pressed laterally on the cranks) and I was sure that it was still the thing causing it.  Then I finally got a new wheelset last week, and the creaking is gone...  go figure

I have had bottom bracket creaks that turned out to be seatpost creaks.  

Echoing Duncann, it can be surprising where the creak actually originates from. I've found success cleaning out my seatpost / seat-tube before.

Is it definitely the cranks? I've never had it but I've read a few accounts of how crank-like creaks were finally traced to rear wheel skewers... seems odd but might be worth 30 seconds of your time to check/grease yours.

You may have a square taper BB -  the cranks' inner taper faces sometimes wear so that there's a bit of movement and creaking. It's difficulto to see and resolve (with light attention from a file) but might be worth removing the cranks and looking at how they've worn, then cleaning and replacing them. Whether the tapers should be greased is a matter I dare not raise (try Google).

Yep, consider investing in either a wheels manufacturing threadfit adaptor, or one of the enduro bearings ones. Both last lifetimes without creaking.

There are many press fit conversion adapter s. They screw together to create a one piece bearing set, usually with replaceable bearings.

Or like many riders sick to death of pressfit BB bought a bike with good old English threaded bearings.

Is it a press fit bottom bracket? If so then you can try removing the bearing cups, greasing them up and pressing them back into the frame. Its probably a job for a bike shop if you dont have the correct tools. Press fit bottom brackets are famous for creaking.