Vehicle noise progressively gotten worse?

My jeep has been making this sound for a few weeks. Last Thursday I had the brakes replaced and oil changed, thinking the brakes were making the sound. My mechanic is telling me the sound is coming from the passenger rear suspension that is loose. When I drive, I notice it closer to the front driver's side. It only happens when hitting the gas, once I get over 30 mph it’s less noticeable. It has progressively gotten worse over the few weeks.