Humming noise at forty five mph

Specifically forty five mph, relatively loud humming sound. Starts forty mph, quits at above fifty five mph. There is a very slight vibration forty five mph also. Almost not noticeable. Sounds like the humming of wind blowing through a ladder tied to roof rack!
Recently changed tires. Yokohama new ones on front, back has about 20,000 on them. All pressures same at 35 psi
Replaced low pressure PS hose about a week ago. Blew while wife driving from long trip. "burped" PS. Just usual grunting when hard L or R at idle, nothing noticeable while driving.
When parked, have tried to mimic sound, holding engine at 1800 rpm, nothing.
Transmission is that goofy six speed, so sloppy shifting, but nothing noticeably different than has been. We just bought a month ago, don't know if fluid/filter has been changed.
Does not seem to change when wiggling the steering wheel. Set the cruise forty five mph, wiggled wheel back and forth, up hill, down, etc. Nothing noticeable.
Help!