Someone linked me this old topic, and I figured out I never noticed those sounds played twice.
This is my fix: (PythonNetworkStreamPhaseGameItem.cpp)
There's no need to play those sounds.
Alternatively (based on penger's but via apply check): (but it's not of my taste) (PythonItem.cpp)
if (c_rkItemData.GetValue(0) == CItemData::APPLY_MOV_SPEED || c_rkItemData.GetValue(0) == CItemData::APPLY_ATT_SPEED)