My '18 PP1 makes the same 'buzzing' noise shifting above 4k, has since day 2... Likely something with the dual disc clutch, not like it should be acceptable but that's likely where it is.
305/30 is gonna be too short in my opinion..I run a 305/35 on a 20x11 in the rear and couldn't be happier..Keep in mind though I'm lowered 1.2" ft and 1.0" rear.
Probably right out the tailpipe...Ford will be the 1st one to 'pull a plug', I'm not touching it for good reason. I'm an old school hot rod guy and would love to start wrenching on it but w/ less than 4k miles on it I'm gonna let the self professed subject matter experts take the lead on it..
THIS ^^^^^^ I cannot stress the importance of resetting the neutral position on ALL pivot points. When you lower the car you place every pivot point bushing in a 'pre-loaded' condition, which is outside of it's required neutral position. You can experience 'bounciness', sway, touchy steering...
I've put 2.5 quarts in mine in 3900 miles! It has both the 'Tick' and a very noticeable 2k rattle, so much so you can hear it over the radio going down the road (4th gear 45mph). It's going to Ford this Friday so we'll see...