Something is creaking on my Cannondale while pedaling with force. It is easier to hear in low gears, when climbing. An audio clip tells it better than any literal description, so here is a recording of me climbing a steep slope: Recording
You can hear it starting from second 7. I held my phone over the crankset.

If it matters, I run Shimano 2x11, FSA MegaExo BB, DT Swiss 350 rear hub. Drivetrain elements such as chain,chainrings,cogs, pulleys are thoroughly cleaned to look and work as new. Some months ago I cleaned and lubed the BB, chainring bolts and pedal threads. The creaking is also happening while standing, so it's not seatpost related. Yesterday I also lubricated the rear wheel nipples(WD40) and also placed a drop of lube on the contact points between the spokes, with no results.
Any ideas ?

bottom bracket?

Chain isn't rubbing anywhere - FD cage? my guess it's a worn chain

Bottom bracket has been serviced some months ago (and is 10 months old, as is the bike). Chain definitely isn't rubbing, and has been replaced in April. According to my gauge it's not 0.75% worn.

Kind of sounds like a chainring noise to me. Sometimes when you install new and you grease the threads, even when they were tightened up good - you might lose one of the bolts then the others start to come loose too.

My bike has 2 chainrings, I can hear the creaks on both rings. I'll still take them apart + grease them tomorrow.

I know that sound, Pull the crank, clean and grease the spindle where it passes through the bearings. Lots of grease, never too much. Did this to my son's bike and my daughters bike, both running that same BB with FSA cranks.

Rest the chain on the BB shell, and see if it's coming from the crank

Doing that too tomorrow. I definitely put some grease there when I serviced the area some months ago.

It's not, the crankarms spin smoothly. Regardless, the creaks are hearable only when pushing with force on the pedals ( ex. climbing)

Who did the BB service? You or a shop? Did they use loctite 609 on the bearings and keep them pressed in when curing?

I did the service, the bike worked fine afterwards. I only used grease.

99% sure the bearings are moving inside the shell. Get new bearings, install with loctite 609. Leaving bearing press on overnight or install the crankset and preload the bearings will the loctite cures

I found the culprit(most likely): it was the cogs digging into the freehub body, as seen in the post here. I imagine the cassette lockring wasn't tight enough. The recommended torque is 50Nm but since I don't have a torque wrench that big, I've tightened it how tight I believed was enough, last time I removed the cassette.
At the time of removing the cassette, I've also greased the derailleur hanger bolt and contact surface, and the skewer, but I believe the noise came from the cassette.
Thanks for your help, guys