First of all. Thanks to you all for all replies and help.
Status as pr. now is that the Surface is working very well. I installed the Citrix Reciever (win32 client) and the USB xHCI drain started again. With uninstall everything went back to being OK again. So I am pretty sure I found (at least one of) the source for this problem on my Surface. I'm guessing other programs can cause the same error as well, as I have seen it posted by many different persons online?!
I installed the Citrix MUI App and it seems to be working a whole lot better, USB xHCI wise. And the MUI is working just fine for my use of the Citrix, so I have not tried to install the win32 client again for tweeking settings, even though it quite possible could be a solution!