ACR INADVERTENTLY CLIMBED OUT OF ASSIGNED ALT.

Narrative

WE WERE FLYING HVT X FROM ORD AND CLRD TO FL330 EXPECTING CLRNC TO FL370. AT APPROX FL320 WE ACKNOWLEDGED A CLRNC TO FL370. APCHING FL340 CHI CENTER ASKED US WHAT OUR ALT WAS. WE REPLIED; 'FL340 CLBING TO FL370.' WE WERE INSTRUCTED TO DES TO FL330 IMMEDIATELY. AT APPROX FL335 WE WERE THEN CLRD TO FL370. PRIOR TO THIS; IN THE EARLY PART OF THE CLB; WE TOLD THE CENTER CTLR THAT HIS TRANSMISSIONS WERE NOT CLEAR; LIKE HE WAS TALKING INSIDE A BARREL. TRANSMISSIONS FROM OTHER ACFT WERE CLEAR. THE CTLR TRIED OTHER MICS AND TRANSMITTERS WITH NO IMPROVEMENT. IN TRYING TO ASSESS THE REASON FOR THE ALT CLRNC MISUNDERSTANDING; WE CONCLUDED THAT WE HAD ACKNOWLEDGED AN ALT CLRNC FOR ANOTHER ACFT. POSSIBLY THAT ACFT ACKNOWLEDGED THE CLRNC AT THE SAME TIME WE DID; THUS BLOCKING CENTER FROM HEARING THE MISTAKE. ANOTHER FACTOR WAS THAT WE HAD JUST RECEIVED A ROUTE CHANGE SO BOTH OF US WERE SOMEWHAT ENGROSSED IN OUR MAPS WHEN THE ALT CLRNC WAS RECEIVED. SUPPLEMENTAL INFORMATION FROM ACN 80230: 2 COMPANY FLTS IN AREA WITH SIMILAR CALL SIGNS WERE ON FREQ. WE BELIEVE BOTH TRIPS READ BACK CLRNC AT SAME TIME SMEARING EACH OTHER.