I've experienced this intermittently as well for some time now (I get "swooshes" and "dings" like mail is being sent and received). It's concerning, because you think perhaps you've been hacked and someone has hijacked your mail program.
It just happened to me now (which is how I found this thread) and so I checked the Console for anything suspicious. There was nothing obviously Mail-related, but this error from Glims (Safari extension) appeared about 8 times right around when the sounds occurred:
2012-08-11 2:43:01.964 PM Safari[9283]: Glims Error: BrowserWindowController not found - Unknown Safari Internal
This may be entirely unrelated to your problem, but perhaps some apps are configured to use these sounds for errors? It's worth taking a look in the Console, you might get some hints as to what's going on.
As for me, I can't see any reason why these Glims errors would be related to these sounds, they just occurred around the same time.
cad
It just happened to me now (which is how I found this thread) and so I checked the Console for anything suspicious. There was nothing obviously Mail-related, but this error from Glims (Safari extension) appeared about 8 times right around when the sounds occurred:
2012-08-11 2:43:01.964 PM Safari[9283]: Glims Error: BrowserWindowController not found - Unknown Safari Internal
This may be entirely unrelated to your problem, but perhaps some apps are configured to use these sounds for errors? It's worth taking a look in the Console, you might get some hints as to what's going on.
As for me, I can't see any reason why these Glims errors would be related to these sounds, they just occurred around the same time.
cad