I have the same hum from my front tire. I purchased in 2014 DL1000 '14 model and after one week put Michelin Pilot Road 4, and hum started immediately. When I sold the bike in September 2017, it was on its 3rd front Michelin PR4 and the hum has never changed. Then I purchased '18 model DL1000 and on my request it came new with PR4 front and rear, and guess what, the hum is there, again.
So, from my point of view, it's tire related. In my case it was always PR4 front and rear but the hum is only coming from the front.
By the way, PR4 comes only in "Trail" version for the front and for the rear you can choose between "Trail" and "non-Trail". I've always had "non-Trail" on the rear and no hum. So, it must be because of "Trail" version of front tire.
2017 DL1000 White
2014 DL1000 Red (sold)
2012 DL650 White (sold)