ALL TIME ERROR NOTED WHEN WARNING HORN SOUNDED AND AIRSPD INDICATOR BECAME ERRATIC. PLT DEDUCED STATIC LINE PROBLEM. SWITCHED TO ALTERNATE STATIC. INSTS BACK TO NORMAL. RECOVERED 6000 CRUISE ALT.

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WX VFR WITH A BRIEF CLB THROUGH SNOW FLURRIES TO THE ASSIGNED ALT OF 6000. CONDITIONS 10 NM N OF ENO WERE VFR AND CAVU. JUST BEFORE ARRIVING OVER ENO; A WARNING HORN BEGAN SOUNDING AND CONTINUED TO SOUND... I ASSUMED IT WAS THE GEAR WARNING HORN. IT WAS PERPLEXING BECAUSE I HAD NOT RETARDED THE THROTTLE. IN SCANNING THE PANEL; I NOTICED MY AIRSPD INDICATOR SHOWED A MUCH HIGHER SPD THAN WAS POSSIBLE. THIS LED ME TO BELIEVE I HAD A STATIC AIR PROBLEM. I ENGAGED THE ALTERNATE STATIC AIR SOURCE AND IMMEDIATELY THE ALT JUMPED TO 8000 AND THE WARNING HORN STOPPED SOUNDING. I IMMEDIATELY CONTACTED DOVER APCH AND ADVISED THEM THAT I HAD A STATIC AIR PROBLEM AND THAT AFTER ENGAGING THE ALTERNATE STATIC AIR SOURCE; MY ALTIMETER SUDDENLY READ 8000. DOVER APCH CONFIRMED AT THIS TIME THAT THEY ALSO READ MY ALT AT 8000. I ANNOUNCED THAT I WOULD DSND TO 6000 WITH DOVER'S APPROVAL AND DID SO. CONTRIBUTING FACTORS: TUESDAY NIGHT WAS A HOWLER IN THE WILMINGTON-PHILADELPHIA AREA WITH HIGH AND GUSTY WINDS AND RAIN. WEDNESDAY MORNING WAS BRIGHT AND VERY COLD WITH A BRISK SW WIND. THE CLB TO 6000 BROUGHT ME INTO VERY COLD AIR...10 DEGS CENTIGRADE. I IMAGINE THAT SOME WATER MUST HAVE GOTTEN INTO THE STATIC SYS AND FROZE IN THE VERY COLD AIR. IN THE PREFLT INSPECTION I DRAINED THE 2 STATIC SYS DRAINS BUT NO WATER WAS RELEASED...THIS WAS NOT SURPRISING SINCE IT WAS VERY COLD AND NEVER IN THE PAST HAD ANY WATER BEEN RELEASED ON DRAINING THE STATIC SYS.