ATC FLC MISCOM ON ALT CLRNC. ATC INTERVENED WHEN FLC DSNDED BELOW ASSIGNED. PF SAID HE READ BACK THE ALT THAT HE HEARD AND ATC DIDN'T CORRECT THE ERROR.

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DURING AN INSTRUCTIONAL FLT BEING CONDUCTED FOR THE PURPOSE OF PROFICIENCY AND RECURRENT TRAINING OF A RATED PLT; TPA APCH CTL ISSUED A CLRNC TO DSND TO 2600 FT. THIS CLRNC WAS MISINTERP AS BEING A CLRNC TO DSND TO 2000 FT. THE ACFT WAS ON AN IFR FLT PLAN AND WAS BEING FLOWN WITH THE PLT BEING TRAINED IN THE L SEAT - HE WAS ALSO WORKING THE RADIOS. AS WE WERE LEAVING 3000 FT I ASKED THE PLT AT THE CTLS WHAT ALT HE WAS CLRED TO. HE SAID 2000 FT. THE CTLR ADVISED THAT WE SHOULD HAVE STOPPED OUR DSCNT AT 2600 FT. WE IMMEDIATELY CLBED TO THE PROPER ALT. THE PF LATER SAID HE THOUGHT HE HAD READ BACK 2000 FT WHEN CLRED. CONTRIBUTING FACTORS INCLUDED A CEILING OF BROKEN CLOUDS AT 3000 FT AND THE CTLR'S INQUIRY AS TO OUR FLT CONDITIONS. ALSO; THE COCKPIT WAS NOISY; MAKING COMS BTWN THE OTHER PLT AND MYSELF DIFFICULT AND MAKING MY MIKE UNUSABLE FOR ATC COMS (UNREADABLE). COCKPIT NOISE REDUCTION; AN INTERCOM SYS AND BETTER ATTN TO ATC INSTRUCTIONS; DESPITE DISTRACTIONS; WILL PREVENT FUTURE OCCURRENCES.