What was found
"ON TAXI TO GATE, AIRCRAFT BEHIND US REPORTED DARK ABNORMAL EXHAUST OUT OF APU, APU WAS SHUT DOWN WITH NO ABNORMAL INDICATIONS." REMOVED FROM SERVICE. OPERATIONAL CHECK OF APU IAW E175 AMM 49-10-00-700-801-A. NO SMOKE NOTED, ALL OTHER PARAMETERS NOMINAL. COULD NOT DUPLICATE. MO PARTS REPLACED.