Rear brake noise - not a squeal

[wdkwang]

Hi everyone,

2010 with ~55k miles. I've changed the front brake pad/rotors once before but never touched the rear brakes since they still had a lot of meat left about 25k miles ago. For the past 2 weeks, I've been wearing a weird low noise coming from the rear of the car while slow speeding driving and coming to a stop such as stop lights or stop signs. It's not a squealing noise which is the usual norm when pads are low and there isn't any noticeable degrade in braking performance either. Any thoughts on what this may be or anyone who've experienced this before?

Thanks