A B737-400 CABIN ALT WARNING HORN SOUNDED AT FL330. THE CREW BEGAN AN EMER DSCNT AND DIVERTED.

Narrative

WE HAD JUST LEVELED OFF AT FL330 ON OUR WAY TO ZZZ2 ON A FLT OUT OF ZZZ1. WE WERE AT OR CLOSE TO ABC INTXN ON FLT PLAN RTE. WE THEN GOT THE CABIN ALT WARNING HORN; AND I SAW THE CABIN ALT WAS AT 10000 FT AND THE RATE OF CLB WAS 1000 FT PER MINUTE. WE DONNED OUR OXYGEN MASKS AND ESTABLISHED COMMUNICATIONS. I ASKED THE FO TO ASK ATC FOR LOWER AND DIVERT TO ZZZ3. WE THEN PROCEEDED WITH THE QRC; QRH PROCS AND EMER DSCNT PROCS AND A DIVERSION TO ZZZ3. ONCE THE FO COMPLETED THE ITEMS REQUIRED ON CHKLISTS AND WE HAD GOTTEN TO A LOWER ALT; HE ASKED THE FLT ATTENDANTS IF ANY PAX OR CREW WAS HAVING DISCOMFORT FROM THE DSCNT. ONLY ONE PAX COMPLAINED OF ANY PROBS. WE ACCOMPLISHED THE DSCNT AND APCH CHKS WERE VECTORED FOR THE ILS TO RWY 34R AND LANDED UNEVENTFULLY. THE EMTS MET ACFT AT GATE AND GAVE ASSISTANCE TO ANY PAX THAT REQUESTED IT. FROM WHAT I WAS TOLD THIS IS A REPEAT PROB WITH THE ACFT. WHAT NEEDS TO BE DONE IS FOR MAINT TO FIND THE PROB AND CORRECT IT. AND IF THIS MEANS TAKING IT OUT OF SVC TILL THAT HAPPENS; SO BE IT.