Air Carrier Captain reported a fume event during preflight at departure gate. Reporter requested maintenance resulting in the aircraft being removed from service.

Narrative

This event occurred while parked at gate XX in ZZZZ before blocking out. The L1 aircraft door was never closed during this event. Aircraft X arrived in ZZZZ with a write up from the previous leg. The turning inflight #1 [Flight Attendant] informed me of a loud air noise coming from the main cabin floor mid cabin approx row 13 ABC on aircraft left. I mentioned this to station maintenance. I did not make a logbook entry at this time because maintenance had the logbook. Maintenance added MEL XX-XX-XB for the logbook write up. The APU was running with the APU bleed ON. Maintenance turned off the packs and left APU running and APU bleed ON while investigating the air noise. When Maintenance brought the signed off logbook back to the aircraft they told me the air noise in the cabin went away. When ground ops pulled the ground air we turned the packs back on. They had been off for approx 30 mins with the APU on and APU bleed on. [Flight Attendant] informed me that the loud air sound was still present after we turned the packs back on. We called maintenance back to the aircraft. Maintenance did not give a good explanation for the abnormally loud air noise from the floor of the mid-cabin and agreed that it was an abnormally loud air noise so I made a logbook write up for the noise. I also noticed a strong dirty socks odor shortly after we turned the packs back on. The First Officer stated that he did not smell it but all inflight told me it was a strong odor which was throughout the aircraft but stronger near mid cabin. I told maintenance about the dirty socks odor after I handed them the logbook but didn't write it in the logbook because they already had the logbook. Maintenance then took the aircraft out of service. I didn't remember to run the cockpit/ cabin odor recognition and isolation guidance procedure.