Integrated handlebar click/ting noise

Hey everyone,

I have an issue that is driving me up the wall as I can't find the reason for it. (This is my first bike that I've built by myself and it has an integrated handlebar.) I noticed on the trainer (also happens off the trainer) that if I really put my weight down on the hoods it clicks/tings once at in the middle, at the steerer tube. Then not doing it again until a while, or if I pull up heavy on it and then putting my weight down again. Things I tried:

• cleaning, regreasing the bearings.
• cleaning, greasing the stem bolts. Also replaced them.
• torquing down everything again.
• trying the test with the top cap removed.
• trying it with the stem bolts loosened.

Right now there is grease on the bolts, on the bearings and that's all. No carbon paste or anything else on other parts of the assembly. During braking, or forward pushing by pulling the brakes there is no clicking, so I think the preload is OK, the assembly is tightly pulled together. During cleanup I checked the bearings and they also run smoothly. Also can't see, notice, hear any cracks with the tap hammer.

Does anyone has any idea what else can it be, or what did I miss?

Thank you!