B757-200 CREW HAD FALSE GPWS TERRAIN WARNING DESCENDING INTO DTW CLASS B.

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FLT WAS CLRED OUT OF 12000 FT TO 6000. PASSING 8500 FT RECEIVED A GPWS WARNING 'TERRAIN TERRAIN... PULL UP... PULL UP...' PF STOPPED THE RATE OF DESCENT AND CLIMBED IMMEDIATELY TO 10000 FT. AS CLB WAS INITIATED THE ADI INDICATED 800 FT AGL ON THE RADAR ALTIMETER AND DESCENDING. ATC VERIFIED PRESENT ALTITUDE ONCE LEVELED OFF AT 10000 FT AND CURRENT/CORRECT ALTIMETER SETTING 30.02. THEY ALSO VERIFIED THAT THERE WAS NOT OTHER ACFT WITHIN CLOSE PROXIMITY OF THE ACFT AT THE TIME OF OCCURRENCE. ONCE LEVEL ALL GPWS WARNINGS WENT AWAY AND ACFT STABILIZED; WE CONTINUED THE DESCENT TO 6000 FT AND PROCEEDED TO DTW WITHOUT ANY FURTHER PROBS OR ALERTS. AN AIRBUS THAT WE WERE FOLLOWING CAME UP ON THE RADIO AND SAID 'THEY RECEIVED THE SAME COCKPIT WARNINGS AND FELT THAT IT WAS DUE TO THE PRECIPITATION.' ADDITIONALLY A B757 ACFT AHEAD ON THE APCH HAD A MOMENTARY GEAR NOT DOWN EICAS INDICATION ON DESCENT. SPEAKING WITH THE ACFT'S CAPT HE SAID THAT THE EICAS MSG WAS MOMENTARY AND IMMEDIATELY WENT AWAY WITHOUT ANY ADDITIONAL OCCURRENCE. THE CAPT MENTIONED HE RECEIVED A 'GEAR NOT DOWN' EICAS MSG AND WAS ACCOMPANIED BY SPURIOUS READING ON THE RADAR ALTIMETER OF 1500 FT WHEN AT AN ALTITUDE OF APPROX 8000 FT. I NEED TO STRESS THE FACT THAT THIS WAS IN CONTINUOUS LIGHT TO OCCASIONAL MODERATE RAIN. NOT SEVERE PRECIPITATION CONDITIONS. I FEEL THAT THIS COULD HAVE CAUSED ADDITIONAL PROBS FOR ACFT ON THE EARLY MORNING ARRIVAL IN DTW. (INITIATING CLB WITH CLRNC TO DESCEND... NOT A GOOD THING) ADDITIONALLY WITH THE COMMENT FROM ANOTHER GLASS ACFT (A-320)... 'THAT WAS JUST DUE TO PRECIPITATION.' THIS STATEMENT COULD LEAD CREWS TO DISREGARD GPWS WARNINGS AT LOWER ALTITUDES BECAUSE THEY BELIEVE THAT IT WAS DUE TO HEAVY RAIN.