With the new sounds introduced in 16w03a, there was a new chest open/close sound introduced. This sound was not applied to Ender Chests also, or if it was, it's no longer a working change.
Linked issues
duplicates 1
is duplicated by 5
Comments 3
merged with MC-91091
In sounds.json, chests use e.g. the block/chest/close variants whereas enderchest uses random/chestclosed (dunno what is intended)