Sometimes when several system sounds play at once, Windows 7 will forcibly lower their volume even though I have disabled automatic volume reduction in Sound -> Communications.
In my case, I have sounds set to play when a program opens or closes. Whenever a UAC prompt appears it often causes the issue because it plays program start, UAC notification, and program stop sounds all at once. I never use any kind of audio communication on my computer so I can only guess this is something else. I have seen this problem occasionally for years, across different hardware. Is there any known tweak/hack for stopping this or any confirmation that it can't be fixed?