Car is making a rumbling sound?

Recently when I brake my car makes a loud rumbling sound that sounds like it's coming from the back. The brake pads were replaced two months ago and though this car is a daily driver it's not used excessively. Mostly to university, the gym, and back. Errands in between of course but only around town. I'm also hearing the rumbling when I park. My car can be parked for 20 minutes and you will hear it rumbling. My driveway is sloped so it almost made me wonder if the brakes are struggling to hold it. It's a 2003 Honda Civic everything's up to date. Does anyone have any idea what this could be?

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