This appears to play on my Windows 7 (64 Bit, Ultimate) PC. Preferably around 15:30, 17:30 and 22:00. Sometimes not at all. I suspect a virus/trojan etc. to be running. Possibly it's also just a sound from a program or browser component. Usually there are running:
The OS, Mozilla Firefox with several Plugins, Skype, Mozilla Thunderbird, Avira Free Antivirus, Total Commander.
Does anybody know this sound or have an idea where it might come from?
Please contact me, thank you!

Pfirsicheisen