Z270m Extreme4 Slow post time

Hey guys my first time here, but not first time with asrock, so far i'm enjoying this great piece of hardware, only thing it's bothering me is the slow post time

it takes around 10 seconds or so to pass the post time and start loading the windows.
and besides that whenever i enter uefi it is sluggish and not responsive as it should be and i have to constantly press DEL, or F11 or whatever i need to press to get into another screen, it's like old time bios trying to read old IDE disks, or counting RAM....

after some experiments, disconnect this and that, i found out that the culprit is the USB 3.0 header.
i have a Dead Silence Cube as my case and even with nothing connected to the 2 USB ports (the external ones through USB header) the post time is slow, and the UEFI is sluggish.

any tips?

my specs are:
z270m extreme 4 UEFI 2.10
i5 - 7600k
2x8gb teamgroup
3 TB seagate
256 sandisk extreme II (main drive)