Also mnopsc1b I have a new theory I have been mulling over-

To what extent could a part of the "northern han"-like influence in Koreans, have actually been from non-Sinitic SinoTibetan groups living in the area? 

I have the following clues that one could have existed:

1) Starting in the middle neolithic, West Liao River cultures became increasingly UpperYellowRiver-like (previously were more Tungusic-like) and by the late neolithic, could be mostly modeled by Upper Yellow River or even just Shanxi Han. But this group is quite far from the "Chinese" cultural center (this area was not even "Chinese" until mid/late Zhou). 

2) Chinese records show that instead, a group called "Shanrong" was living in northeast Hebei until they were conquered in the warring states period (https://en.wikipedia.org/wiki/Shanrong). "Rong" also tends to denote Tibeto-Burman-ish peoples? So it is possible whoever lived here could just be an independent Sino-Tibetan group. 

3) Manchu/Xibo are majority "Chinese-like", but it would be rather difficult for Tungusics to assimilate en-masse actual Chinese people who have a strong centralized culture. Instead, if they were living more like decentralized Tibeto-Burman bands, it would be easier to assimilate and Tungusize them. 

4) The Chinese-like autosomal proportion of Koreans can be quite high, but I do not know if the population from Han commanderies or later sparse migrants would be enough to bring it up that much. It could be possible that something northern Han-like, but not actually "Chinese", got into the Korean genome en-masse at one point? 

Hence, I theorize now that there could have been a non-Sinitic (or at least "Chinese mainstream"), but still Sino-Tibetan group living in the northeast Hebei, north Liaoning area that were later assimilated into Goguryeo (in the east), Tungusics (from the north), and bulk Chinese (in the west). 

However, this would also imply that there could be non-Sino-Xenic but still Sino-Tibetan loanwords in the Korean language. Do you know if it would be possible to detect anything like this? Ie. something Old Chinese or Tibeto-Burman like?