Narrative:

While climbing out of ZZZ we observed a pressure squeal from first officer R2 sliding window at 9000 feet MSL. I have observed pressure leaks on prior flights but this one was exceptionally loud and rather alarming. Climbing out of 10;000 feet we conducted the climb checklist where we verified that the aircraft was pressurizing properly. The leak was clearly coming from my R2 window and I ensured that the window was secure/closed and could not feel any air rushing around the window. The captain and I decided to continue climbing as pressurization; outflow valve; and control panels all were normal in hope that the leak would close as was common with leaks observed in past flights. However; in this case; as we obtained clearance to FL230; it was clear that this leak was not closing and was extremely loud and even painful to our hearing. We discussed the problem; and faced with an extended over water flight duration planned at FL410; we determined the risk was too high to continue flight and the captain directed that we divert to ZZZ1.as with any unplanned diversion and dealing with the physiological distraction/unpleasant noise; task saturation was a consideration and the noise an additive crew factor. We began [dividing] up tasks to decrease workload and the captain handled flying and talking with cabin while I worked with ATC and handled FMC programming and dispatch communication. I informed ATC of the need to stop climbing and divert to ZZZ1. We did not not declare an emergency. Center issued new clearance to ZZZ1 including an arrival transition and I set up the automation for arrival into ZZZ1 while the captain informed the flight attendants and passengers of the situation. Aircraft landing weight was not a consideration; which allowed a prompt landing into ZZZ1. We completed the diversion plan and other checklists/briefings and received proper authorization form dispatch via ACARS. During final approach we observed the pressure leak finally cease at 5000 feet MSL. Maintenance met the aircraft when we arrived at ZZZ1.a quick assessment by maintenance determined that the window seal drain hose had become stuck in the window after closure. Upon further inspection the mechanic determined that the drain hose was not an FAA approved part and had no part number. The hose was very flexible and appeared to have no rigidity. He explained that this should be a dark grey rigid hose that is not bendable. Instead; this hose had a very flimsy structure and resembled a surgical rubber hose of some type. Clearly; it was not able to properly fit in the designated area near the window which allowed it to interfere with side window operation. Operations made arrangements for an aircraft swap and we deplaned the passengers and cargo. Flight was completed on a new aircraft approximately 1:40 minutes behind original schedule.I would suggest measures be taken to ensure window seal drain hoses are of approved composition/installation and do not interfere with window operation.

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Original NASA ASRS Text

Title: B737-700 flight crew reported diverting due to a cockpit window air leak.

Narrative: While climbing out of ZZZ we observed a pressure squeal from First Officer R2 sliding window at 9000 feet MSL. I have observed pressure leaks on prior flights but this one was exceptionally loud and rather alarming. Climbing out of 10;000 feet we conducted the Climb Checklist where we verified that the aircraft was pressurizing properly. The leak was clearly coming from my R2 window and I ensured that the window was secure/closed and could not feel any air rushing around the window. The Captain and I decided to continue climbing as pressurization; outflow valve; and control panels all were normal in hope that the leak would close as was common with leaks observed in past flights. However; in this case; as we obtained clearance to FL230; it was clear that this leak was not closing and was extremely loud and even painful to our hearing. We discussed the problem; and faced with an extended over water flight duration planned at FL410; we determined the risk was too high to continue flight and the Captain directed that we divert to ZZZ1.As with any unplanned diversion and dealing with the physiological distraction/unpleasant noise; task saturation was a consideration and the noise an additive crew factor. We began [dividing] up tasks to decrease workload and the Captain handled flying and talking with cabin while I worked with ATC and handled FMC programming and Dispatch communication. I informed ATC of the need to stop climbing and divert to ZZZ1. We did not not declare an emergency. Center issued new clearance to ZZZ1 including an arrival transition and I set up the automation for arrival into ZZZ1 while the Captain informed the flight attendants and passengers of the situation. Aircraft landing weight was not a consideration; which allowed a prompt landing into ZZZ1. We completed the diversion plan and other checklists/briefings and received proper authorization form Dispatch via ACARS. During final approach we observed the pressure leak finally cease at 5000 feet MSL. Maintenance met the aircraft when we arrived at ZZZ1.A quick assessment by Maintenance determined that the window seal drain hose had become stuck in the window after closure. Upon further inspection the mechanic determined that the drain hose was not an FAA approved part and had no part number. The hose was very flexible and appeared to have no rigidity. He explained that this should be a dark grey rigid hose that is not bendable. Instead; this hose had a very flimsy structure and resembled a surgical rubber hose of some type. Clearly; it was not able to properly fit in the designated area near the window which allowed it to interfere with side window operation. Operations made arrangements for an aircraft swap and we deplaned the passengers and cargo. Flight was completed on a new aircraft approximately 1:40 minutes behind original schedule.I would suggest measures be taken to ensure window seal drain hoses are of approved composition/installation and do not interfere with window operation.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.