B757-200
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Confusion; Distraction; Troubleshooting
Aircraft Equipment Problem Critical
Flight Crew Landed in Emergency Condition
Manuals; Aircraft
Just prior to top of descent; an aural tone began chiming in three short beeps. It continued chiming 3-4 four times as the PF (Pilot Flying) and I searched for the cause. The fifth time the beeping occurred it was followed by a MASTER CAUTION light.I attempted several times to cancel the light and beeping by pressing the light.No systems appeared to be faulting as both the PF FO (First Officer) and I began scanning all instruments and systems including the overhead and status page for indications of a system failure. All systems appeared to be operating within normal parameters; and no other advisory lights illuminated. Unable to determine the cause of the Illuminating MASTER CAUTION LIGHT and unable to cancel the alert; I [advised ATC]. Continuous beeping and steady CAUTION light for continued for 10-15 minutes. NOTE: There isn't anything in the 757 QRH for such a situation.While reaching for my iPad the entire mount fell and knocked out the lead plug in for my headset and I was momentarily unable to transmit or receive and went to speaker and hand-held microphone. It was not until after shutdown at the gate that I determined the source of communication failure.Passing through 10;000 ft. we finally received a status message which read EICAS DISAGREE. I was also able to cancel the MASTER CAUTION and aural tone. There isn't anything in the 757 QRH for an EICAS DISAGREE situation either.Uneventful approach and touchdown ensued.I have no clue as to why the MASTER CAUTION LIGHT didn't appear when the beeping first began. Then it took several minutes of the beeping before the EICAS DISAGREE status message appeared. I was unable to find anything in the QRH concerning a MASTER CAUTION Light without any other indications; or EICAS DISAGREE Status message. Testing the light bulbs all illuminated as they should.
B757 Captain reported observing a 'Master Caution' chime and light without any associated indication of a system malfunction.