2003 Protege Vibration Under Driver's Side

Mechanic checked this out and tells me it's not the wheels, axle, or bearings, and won't open up automatic trans unless I am ready to fork out plenty-o-cash for the anticipated "repairs". Fairly new tires, re-balanced about a month ago and rotated. Vibration started before rotation, but it was on the passenger side before it transferred over to the driver's side after the rotation. If there's a problem with the wheel(s), shouldn't he have caught it when he balanced the tires? It's speed-dependent: Steering wheel doesn't vibrate & vibration starts around 35 mph and gets pretty loud up to 45 mph, then diminishes above 55 mph. (Also somewhat time-dependent, doesn't become noticeable until I've been driving the car for at least 20 minutes.) Otherwise the car runs well and the gears don't feel like they are slipping.

Check your motor mounts.

what kind of tires do you have? you can still have tires on your wheels that cause a vibration. especially if it transferred from one side to the other. id have the technician re-check the balance and see if the wheel is out of round.

Were the tires/wheels balanced on a Roadforce balancer? If not, go to a shop that has one. Older Miatas have the same problem unless this type of balancer is used.

I ALWAYS have my tires roadforce balanced. Makes a HUGE difference. might me a slightly slipped belt or busted belt. In my days of being a tire technician, I've had a few "headscratcher" cars that always came back for vibration. only way to figure out which wheel is to rotate them around the car and see which tire follows.