I recently noticed something very weird: every time I connect a removable device such as USB flash drive or external HDD or even my smartphone, the sound volume goes down to 5% but only for the browser & mediaplayer. I can change the sound volume using volume mixer but it's annoying doing so every time I connect something to my PC.
I reinstalled the drivers
for my sound card & for every device I usually connect & also I reinstalled the browser(Opera browser) & Winamp without luck.
Also, I had some problems in the past that might be related to this one. After installing SP1 every time I logged into windows I was notified that Audio Service is not running although it was running. (solved this one).
Another problem was related to USB removable devices. Apparently Windows was unable to assign letters to all my removable devices, even if I manually assigned a letter to a certain device. I didn't solve this one, however I use USB Safely Remove to assign letters and it seams to be working fine so far. ( Windows 7 does not assign drive letters to external HDDs