Rashi on Numbers 4:47/רש"י על במדבר ד׳:מ״ז

1עבדת עבדה THE SERVICE OF THE MINISTRY — (lit., a service of a service). This is the song of the Levites with accompaniment of cymbals and harps, this being the service attached to another service (the sacrificial service) (Arakhin 11a).

2ועבדת משא is what it literally implies: AND THE SERVICE OF CARRYING.