A320 Flight Attendant reported that during climb; they heard a loud rumbling noise and felt vibrations in the floor. Flight Attendant advised the pilots and the flight returned to departure airport.

Narrative

After level off; I (Flight Attendant 4) proceeded from my jumpseat to the aft galley to prepare for service. Sat in jumpseat at 4R door. Aircraft continued climbing and door began making a loud; low; mechanical rumbling noise. Noise got louder. Strapped myself in and asked Flight Attendant 2 if she could hear the noise. She came over to the door and could also hear the noise. Did not sound normal/we had never heard anything like it. I proceeded to call the Flight Deck to advise them of the issue. Captain said he would call back. Captain called back; asked me to describe the noise again. Noise had dissipated in the several minutes between; but reoccurred when altitude/adjustments were made. The three beverage carts aircraft right were also noticeably shaking/vibrating; while those on aircraft left sat still. Vibrations could be felt in floor near aircraft right slide bustle and when placing one's palm on the door or adjacent fuselage. Decision was made to return to ZZZ. Captain advised us of a precautionary landing protocol. Strapped myself in at my original jumpseat and completed 30 Second Review. Aircraft was able to taxi safely back to terminal. Passengers remained onboard and mechanic boarded. I explained situation to the mechanic in aft galley. Mechanic asked if it could have been someone in the lavatory. No one entered the aft aircraft right lavatory during the initial incident. This was an abnormal sound; emanating from the 4R door/the surrounding area. In nine years of flying; I have never heard something similar.Captain called me forward to describe the incident one more time for the official logbook. Ground Supervisor came into Flight Deck during this and interrupted Captain twice about extending his duty day and switching aircraft; before the initial safety write up could be completed. Captain asked him to step back. Safety protocols then continued to be followed to completion.Captain later informed us that this aircraft had previously been written up for the same issue. He read us the original write up; and several parts were nearly verbatim. Loud; low mechanical noise starting around 17;000 ft. This aircraft needs to be removed from service until such time as the issue is fully identified and repaired. The aircraft was initially reassigned to us the next day (less than 24 hours later) having been sitting in a non-hub station and inspected by maintenance who originally asked us if the door noise and vibrations could have been caused by a passenger in the lavatory. The problem has obviously been detected before and remained unsolved.