abc1234

I have a 04' RX330 with about 10,000 miles on it. Recently, I heard buzzing noise from back of the car when car is in low speed (40 miles or under). This buzzing noise is kind like mosquito sound but is on and off. I am not sure is this caused by noise from tires or it is something else. As far as I know, I did not hear this noise until 2-3 weeks ago. Is anyone experiencing similar problem? Any advise will be greatly apprecited!!!