I've got a Mazda 3 sedan 2.5 with manual transmission. I've had the car about 1 1/2 years and it's been a great little car, but in the last 2 weeks or so it has developed a humming noise. Sounds kind of like noisy tires, but just started out of nowhere. I've checked the front wheel bearings and axels and everything seems solid. I'll be checking the rear wheel bearings tomorrow morning (it's 95° right now), but I don't think that's gonna be the problem as it sounds like it's coming from the front of the car. Could it be transmission? I've never checked or replaced the fluid as the car has always shifted fine and still does. The car has about 160,000 miles. Any advice would be appreciated.