A B737-300 Captain reported a loud squeal coming from the forward side of his glareshield during a departure climb making communications unacceptable at altitude. Maintenance later determined the bottom row of screws were loose at the left (L-1) forward windshield. Captain notes aircraft had just come out of an A-Check.

Narrative

This concerns the flight just a few hours previous. As we climbed; enroute from ZZZ to ZZZ1; a squeal started from what seemed to us the front of the glare shield by the forward windscreen. At altitude it became unacceptable with both pilots using earplugs and ATC commenting on the noise during radio transmissions. We both suspected an Air Conditioning (AC) ducting problem; but were unable to identify exactly what it was. Descending around 12000 feet to 10000 feet with the cabin PSI coming down below about 5.5 the squeal went away. Turns out the bottom row of screws on the Captain's forward windscreen (I believe referred to as L1) were loose. The aircraft had just come from the hanger in ZZZ after an A-Check. Can the Safety Investigator check into this and find out if the windscreen was replaced and what does a job card procedure have with something like this. Or was something else done on an A-Check requiring something with the windows and is there a procedure for inspection afterwards.