Gulfstream G200 pilot reported main cabin door seal malfunction during departure. Flight crew returned to departure airport.

Narrative

Aircraft X was prepared for a night flight from ZZZZ to ZZZ carrying 4 passengers departing at XA:00 pm local time. The crew arrived to the airport .A normal preflight routine was executed. Normal flight plan was accepted. Passengers were loaded and a normal taxi and departure was made from runway XX from ZZZZ. Passing 3;000 ZZZZ Control handed Aircraft X to ZZZ Center on XXX.X. The flight crew checked in and was turned direct ZZZ1 and was given a climb clearance to maintain FL270. Leaving 10;000ft the pilot flying noticed a LOUD hissing/squealing noise coming from the main door area; not noticed during prior flights. The pilot flying consulted the pilot monitoring 'Do you hear that?'One ear piece was removed from the pilots ears to listen closer. The pilots determined the noise was being produced from the main cabin door area; and checked the pressurization system and the pressurization schedule in the QRH. At this time everything was normal. Leaving FL190 the noise increased in intensity and the pilot monitoring left his station to investigate closer. Climbing through FL230 ZZZ [Center] gave clearance for 'Aircraft X Climb and maintain FL400' The Pilot Flying responded 'ZZZ Center standby; Aircraft X is requesting to level at FL 240; Standby' .Center responded 'Copy Aircraft X; amend altitude; maintain FL240. Is everything Okay?' 'At the moment yes; maintain FL240 Aircraft X' The pilot not flying returned to his station and stated that he was not comfortable continuing; and the decision was made unanimously to execute a turn-back WITHOUT declaring an emergency. The Pilot not flying responded to Center 'Center; Aircraft X; we would like to return to the airport; we have an issue with a door seal and would like to return to ZZZZ.' Center asks 'Are you declaring an emergency or do you need any assistance at this time?' 'Negative; everything is okay; we need a cautionary return to ZZZZ.' 'Roger; Aircraft X you are cleared to ZZZZ via DIRECT ZZZZ; descend and Maintain 6;000; contact ZZZZ XXX.Y.' A left turn and a descent was commenced toward ZZZZ. The crew executed a normal approach and landing onto runway XX at ZZZZ. Upon inspection after landing; a large hole was found in the upper left door seal.