screeching/grinding sound when coasting at speed
I think it's impossible for it to be coming from the bottom bracket while the pedals are not turning.  More likely it's coming from the rear hub.

I'd first check whether the spoke guard (if you have one) has come loose and is rubbing against the cluster.  And inspect the area behind the cluster for any piece of trash that has gotten in there.  Failing that, you probably have a problem with your freehub.