When I get to about 40-50mph a vibrating/howling/humming sound starts happening, it goes away around 65-70mph, but you can still hear it with the windows up, it seems to be getting worse. Any ideas what could go wrong to make that happen?
As already mentioned, either tires or wheel bearing are your most probable causes.
If you rule it out to not be tires, make sure you check each bearing (ALL 4!!) with a stethascope to save yourself lots of trouble. You would be amazed how far a noise will travel and where it can "sound" like its coming from.
Also, typically wheel bearing noises will get worse/change/go away when turning, such as getting better/worse when turning left/right or going around a curve. Thats a tell tale sign you have a wheel bearing issue as you add or remove load from a particular bearing.