What was found
R1 WINDOW, LOUD WIND NOISE & WHISTLE FROM TAKEOFF ROLL TO 5000 FT AND 250. DEBRIEFED FLT CREW, LOUD SOUND STARTED AT 100 KNOTS & GREW LOUDER UNTIL 5000FT, STOPPED IN CLIMB. ACFT PRESSURIZED TO A DELTA P OF 2, FOUND TOO LOUD TO CONTINUE FLT. CREW COULDN`T PIN POINT SOURCE ANY CLOSER THAN R1. CREW DID NOT NOTICE ANY EXTRA AIRFLOW FROM AROUND WINDOW. PERFORMED INITIAL LEAK CHKD IAW AMM 5-51-91. NOTICED LEAK AROUND FO SLIDING WINDOW AT 0.2 PSI. INSPECTED & FOUND DRAIN TUBE UNSECURE IN MOUNT, CAUSING WINDOW SEAL ON THE SLIDING WINDOW TO BE DISLODGED ALLOWING IT TO LEAK. SECURED FO SIDE DRAIN TUBE & PERFORMED PRESSURIZATION AGAIN. NO HISSING OR LEAKS HEARD INSIDE CABIN. ACFT PRESSURIZED TO 4 PSI. ACFT OKAY FOR SERVICE.