2005 Toyota Tundra Owners Manual - Page 501
2005 Toyota Tundra Manual
Page 501 highlights
'05 TUNDRA_U (L/O 0408) Leak detection pump This pump performs fuel evaporation leakage check. This check is done approximately five hours after the engine is turned off. So you may hear sound coming from underneath the rear deck for several minutes. It does not indicate a malfunction. x 2005 TUNDRA from Aug. '04 Prod. (OM34427U)