Air carrier Captain reported a cabin depressurization due to a faulty main door seal. The pilots returned to the departure airport where an overweight landing was accomplished.

Narrative

Departed ZZZ XXC; and climbing through about 6000 ft. heard a sudden very loud rushing noise and felt my ears pop. Almost immediately saw the emergency lights turn on and received an emergency call from the forward Flight Attendant. I called for controls and radios and immediately suspected that the main cabin door seal was faulty leading to a loss of pressure. I realized that the cabin altitude emergency decent would not be necessary in this scenario due to our low altitude; and not seeing any additional messages; we searched the QRH; and did not find anything. I was not sure of exactly which QRH procedure to run at this point so I elected to have the First Officer call back to the Flight Attendant to try to better understand the gravity of the situation but unfortunately the noise from the door seal was so loud he was unable to hear anything. I told ATC that we would be leveling off at our pre-assigned altitude of 8000 ft.; that we had lost pressurization and that we would need to return to ZZZ. We received vectors while we ran some checklists. The First Officer was looking for an appropriate checklist while I flew the aircraft and communicated with ATC. Eventually we settled on the unpressurized flight procedure message. In hindsight this may not have been 100 percent correct but I determined that it was the most appropriate under the circumstances and would hopefully prevent landing with an improper pressurization condition should the seal become intact and the cabin suddenly pressurize again. We completed the procedure which alleviated the noise from the door seal and we were finally able to communicate with our cabin crew at which point I relayed the company items; while the First Officer began setting up for the ILS to XXL. At this time I also made a PA announcement explaining that we had suffered a malfunction and would be returning to ZZZ. I briefed the approach and we realized that we would be close to our max landing weight. At this point I elected to configure the aircraft early to increase our fuel burn. We completed a descent checklist; and advised ATC that we were ready to return for landing. Now that things had calmed down somewhat I made one final call to the Flight Attendants to reiterate that there was no need to brace and no plan for evacuation. We landed approximately 300 lbs. overweight at a rate of approximately 200 fpm at touchdown. We cleared the runway; and taxied to the gate without further incident. I was very impressed with the professionalism and performance of my crew.I feel that the startle factor combined with adrenaline may have caused me to overestimate the severity of the situation. I feel that in hindsight we could have easily asked for a momentary delay vector to avoid the overweight landing. I also feel that the selection of emergency depressurization per the QRH was not necessary; and that a manual depressurization using the cabin pressure controller would have been a less drastic way to vent the remaining pressure from the cabin.