Now sounds more or less as expected in macOS 10.16 aka 10.11, where the old system alert sound "Submarine" has been replaced with new sound "Submerge".

Author: jerrykrinock

SSYAlertSounder.m

@@ -126,6 +126,19 @@ - (NSArray*)availableSoundsSorted {
 
 
 - (void)playAlertSoundNamed:(NSString*)name {
+    /* In macOS 10.16 aka macOS 11, the "Submarine" sound has been replaced
+     by a similar sound, "Submerge".  Why, oh Apple, why ?? */
+    if (@available(macOS 10.16, *)) {
+        if ([name isEqualToString:@"Submarine"]) {
+            name = @"Submerge";
+        }
+    }
+    else {
+        if ([name isEqualToString:@"Submerge"]) {
+            name = @"Submarine";
+        }
+    }
+
     if (!name) {
         return ;
     }

SSYSemaphore.h

@@ -245,7 +245,7 @@ float randomPeriod(float min, float max) {
             // there is a BUG in SSYSemaphore.  The whole idea of SSYSemaphore
             // is to prevent such collisions!
             NSLog(@"COLLISION!!  Expected:%@  Read:%@", [self key], readKey) ;
-            [[NSSound soundNamed:@"Submarine"] play] ;
+            [[NSSound soundNamed:@"Submerge"] play] ;
         }
 
         [readKey release] ;