Okay. If it gets faster then clearly it is something spinning that is effected by vehicle speed and not RPM. This means drive shaft, rear end bearings, or a tire.
I would start with inspecting the u joints as that is the most likely on a RWD vehicle like yours. Here is a guide that will help with that:
https://www.2carpros.com/articles/how-u-joints-work
If these check out then the I would move the tires but it sounds like you eliminated a lot of this so a drive shaft is likely.
Dec 29, 2019 at 6:57 PM