2006 Toyota Sequoia Owners Manual - Page 476
2006 Toyota Sequoia Manual
Page 476 highlights
'06_SEQUOIA_U (L/O 0508) 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 luggage compartment for several minutes. It does not indicate a malfunction. x