diff --git a/Sources/removemacai/SelfTest.swift b/Sources/removemacai/SelfTest.swift
index e260482..d284653 100644
--- a/Sources/removemacai/SelfTest.swift
+++ b/Sources/removemacai/SelfTest.swift
@@ -217,6 +217,9 @@ func selfTest() -> Bool {
     program: "/Library/PrivilegedHelperTools/dev.orbstack.OrbStack.privhelper", system: true)
   check(script.owner == "sync.sh" && helper.owner == "OrbStack", "background items are named after what they run")
 
+  check(Storage.soundLibraryUsers(["com.apple.finder": "Finder", "com.example.missing": "Missing"]) == ["Finder"],
+    "apps that share the sound library are found by bundle identifier")
+
   print(failed == 0 ? Term.green("all checks passed") : Term.red("\(failed) failed"))
   return failed == 0
 }
diff --git a/Sources/removemacai/Storage.swift b/Sources/removemacai/Storage.swift
index 59aa3fe..a327216 100644
--- a/Sources/removemacai/Storage.swift
+++ b/Sources/removemacai/Storage.swift
@@ -1,3 +1,4 @@
+import AppKit
 import Foundation
 
 /// Space RemoveMacAI can give back. Files go to the Trash, so nothing is
@@ -38,6 +39,16 @@ enum Storage {
     ("pages", "Pages", []),
   ]
 
+  /// Apps that share GarageBand's sound library, by bundle identifier.
+  static let soundLibraryApps = ["com.apple.logic10": "Logic Pro", "com.apple.mainstage3": "MainStage"]
+
+  /// The sound library apps installed anywhere Launch Services knows of,
+  /// including an external disk.
+  static func soundLibraryUsers(_ apps: [String: String] = soundLibraryApps) -> [String] {
+    apps.filter { !NSWorkspace.shared.urlsForApplications(withBundleIdentifier: $0.key).isEmpty }
+      .map(\.value).sorted()
+  }
+
   /// Finds what can go and how big it is. Slow on big caches; call it off the main thread.
   static func scan() -> [StorageItem] {
     var items: [StorageItem] = []
@@ -90,13 +101,16 @@ enum Storage {
       caveat: "Quit your apps first. Apple's own caches are left alone.",
       paths: children(home + "/Library/Caches").filter { !($0 as NSString).lastPathComponent.hasPrefix("com.apple.") }))
 
+    let sharing = soundLibraryUsers()
     for app in appleApps {
       let path = "/Applications/\(app.app).app"
       guard FileManager.default.fileExists(atPath: path) else { continue }
+      let keepExtra = !app.extra.isEmpty && !sharing.isEmpty
       items.append(files(
         id: app.id, title: app.app,
         detail: "One of Apple's optional apps. It reinstalls free from the App Store.",
-        paths: [path] + app.extra.filter { FileManager.default.fileExists(atPath: $0) }))
+        caveat: keepExtra ? "Its sound library stays, because \(sharing.joined(separator: " and ")) uses it too." : nil,
+        paths: [path] + (keepExtra ? [] : app.extra.filter { FileManager.default.fileExists(atPath: $0) })))
     }
 
     var snapshots = StorageItem(