2005 Toyota Corolla Buzzing/whining noise

Hello, my 2005 Toyota Corolla makes a whining noise that sounds kind of like a mosquito buzzing in my ear. I notice the sound when I am driving 15-25mph and I hear it from the inside of my car. The noise stops when I hit the brakes. I'm not sure if it continues once I speed up, it is kind of a faint sound andt he road noise would cover up the sound. A friend told me it could be the transmission. I have not had my transmission fluid flushed since I bought the car in 2007. Could this be the culprit? Is is something besides the transmission possibly?
Thank you so much!