POOR WX; LARGE VOLUME OF TFC AND CONGESTED ATC FREQS WHEN RPTR ACFT WAS CLRED FROM ABOVE FL180 TO 16000 FT. CTLR DID NOT PROVIDE A LCL ALTIMETER SETTING; BUT FLC THOUGHT THEY HAD PICKED IT UP ON ATIS; WHICH WAS DIFFICULT TO HEAR DUE TO STATIC CAUSED BY LIGHTNING IN THE AREA. CTR CTLR QUESTIONED THEIR ALT WHEN THEY WERE SUPPOSED TO BE LEVEL AT 16000 FT AND THEN THEY REALIZED THEY HAD AN ERRONEOUS ALTIMETER SETTING.

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I WAS ACTING AS CAPT ON THIS FLT. WE WERE BEING VECTORED BY ZAU IN AN AREA OF TSTMS TO PROCEED EVENTUALLY OVER PONTIAC FOR AN APCH TO RWY 9R. THE FREQ IN USE WAS SATURATED WITH REQUESTS FOR DEV AND THERE WAS EXTENSIVE COMPLAINING BY SEVERAL ACFT TO THE CTLR'S INSTRUCTIONS. WE WERE CLRED TO DSND FROM ABOVE FL180 TO 16000 FT. NO ALTIMETER SETTING FOR THE CHAMPAIGN AREA WAS GIVEN PASSING FL180. I CALLED FOR DSCNT CHK. THE FO HAD COPIED THE ATIS AND CALLED OUT 30.49 WHICH WE SET IN BOTH ALTIMETERS. AFTER LEVELING AT 16000 FT; ZAU ASKED WHAT ALT WE WERE AT. AFTER REPLYING 'LEVEL AT 16000 FT;' CTR REPLIED; 'I SHOW YOU AT 15500 FT; CHK ALTIMETER SETTING 29.46; MAINTAIN 16000 FT.' I IMMEDIATELY INITIATED CORRECTIVE ACTION TO LEVEL AT 16000 FT AFTER CHANGING THE ALTIMETER SETTING. TO MY KNOWLEDGE THERE WAS NO CONFLICT WITH OTHER TFC OR COMPROMISE WITH SAFETY. IN REVIEWING THE OCCURRENCE WITH THE FO; HE STATED THAT THE ATIS WAS DIFFICULT TO UNDERSTAND AND BREAKING UP WITH STATIC DUE TO LIGHTNING IN THE AREA. I BELIEVE THIS FACTOR; COUPLED WITH THE HIGH STRESS OF THE SIT FOR BOTH THE CTLR AND US; ACCOUNTED FOR THIS DEV. TO PREVENT RECURRENCE OF THIS SIT; CTLRS SHOULD MAKE A POINT OF INCLUDING THE LCL ALTIMETER SETTING FOR ANY CLRNC BELOW FL180. PLTS SHOULD MAKE A POINT OF NOT ACCEPTING A CLRNC BELOW FL180 WITHOUT RECEIVING THE LCL ALTIMETER SETTING FROM THE CTLR AND THEN XCHK THAT SETTING WITH WHAT IS BEING ADVERTISED ON THE ATIS.