Originally Posted by
Toddnel
Is that what it is? I always wondered what caused that. Delta must either always forget or they must have a different procedure because it always sounds like someone's in the belly changing tires.
FWIW, it's actually a PTU (power transfer unit) that you are hearing. It connects the two main hyd systems (no fluid transfer) so one side can automatically power the other when differential system pressure exists. That's why it sounds like a chainsaw as it instantly cuts in/out repeatedly when one system has slightly less pressure as a result of an engine being shut down.
And yes, it seems many Airbus operators have different procedures to deal with it during single engine taxi or parking.