A D328 FO RPTS A DEAFENING NOISE IN THE COCKPIT THAT LED THE FLC TO DSND WITHOUT A CLRNC FROM CTR. AFTER LNDG; THE CREW DISCOVERED THAT THE NOISE WAS A RESULT OF THE FAILURE OF THE LATCH ON THE OVERHEAD HATCH.

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ALT 16000 FT. ZNY ASKED US TO CHANGE TO HIS OTHER FREQ. AS I WAS ABOUT TO RE-CHK IN ON THIS; A DEAFENING NOISE STARTED IN THE COCKPIT. THE CAPT; WHO WAS FLYING; THOUGHT IT A DECOMPRESSION SIT. I LOOKED FOR INDICATIONS OF THIS -- THERE WERE NONE. COM WAS ALMOST INEFFECTIVE DUE TO THE NOISE. HE TOLD ME HE WAS DSNDING. WE HAD NO IDEA AS TO WHAT WAS CAUSING THE NOISE. I TRIED TO TELL THE CTLR THAT WE WERE INITIATING A DSCNT BUT HE WAS BUSY. WHEN I DID GET THROUGH WE WERE PASSING 15200 FT FOR 10000 FT. THERE WAS NO CONFLICT. MYSELF AND THE CAPT HAD CONCLUDED BY THEN THAT ALL THE SYS WERE OPERATING NORMALLY BUT THAT WE WOULD STILL LIKE 10000 FT AS A PRECAUTION. THE CTLR CLRED US TO 10000 FT AND WAS; ALTOGETHER; VERY HELPFUL. THE REST OF THE TRIP WAS UNEVENTFUL EXCEPT FOR THE DEAFENING NOISE WHICH CONTINUED UNTIL JUST BEFORE WE LANDED. THE CAUSE OF THE NOISE WAS PART OF THE COCKPIT OVERHEAD HATCH HAD BROKEN AWAY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS RPTR STATES THAT HE FIRST CHKED FOR CAUTION AND ADVISORY SYS MESSAGES AND THERE WERE NONE. THE CABIN ALT WAS NOT WAVERING. HE TRIED TO PERSUADE THE CAPT TO WAIT FOR A CLRNC SINCE THERE DID NOT APPEAR TO BE A CRITICAL PROB ASSOCIATED WITH THE NOISE. DURING A LATER REVIEW WITH THE CTLR VIA TELEPHONE; THE CTLR INDICATED THAT HE HAD NO PROB WITH THE DSCNT. THE D328 HATCH IS A PLUG TYPE; SO IT WAS NOT POSSIBLE TO LIFT THE HATCH PHYSICALLY FROM THE ACFT DURING PRESSURIZED FLT. THE HATCH WAS ALSO SECURED BY THE INTERIOR LOCKING PINS. RPTR WILL DECLARE AN EMER NEXT TIME.