The FancyDrop mod's \oxide\config\FancyDrop.json has a whole section about Notifications:
"Notification": {
"Maximum distance in meters to get notified about landed Drop": 700,
"Maximum distance in meters to get notified about looted Drop": 500,
"Notify a player about incoming Drop to his location": true,
"Notify a player about spawned Drop at his location": false,
"Notify admins per chat about player who has thrown SupplySignal ": false,
"Notify console at Drop by SupplySignal": true,
"Notify console at timed-regular Drop": true,
"Notify console when a Drop is being looted": true,
"Notify console when Drop is landed": false,
"Notify console when Drop is spawned": false,
"Notify console when Drop landed/spawned only at the first": true,
"Notify players at custom/event Drop": false,
"Notify players at custom/event Drop including Coords": false,
"Notify players at Drop by SupplySignal": false,
"Notify players at Drop by SupplySignal including Coords ": false,
"Notify players at Massdrop": true,
"Notify players at Random/Timed Drop": true,
"Notify players at Random/Timed Drop including Coords": false,
"Notify players when a Drop is being looted": false,
"Notify players when a Drop is being looted including coords": false,
"Notify players when Drop is landed about distance": true,
"Notify Players who has thrown a SupplySignal": false,
"Notify Players who has thrown a SupplySignal including coords": false,
"use GUI Announcements for any Drop notification": false
},
You also might have Inbound or another plugin that is giving notifications. Also, some of those notifications might only be visible to admins, so check with a non-admin player if they're seeing them too.