And which version of Windows are you using? Is it 64 bit or 32 bit?
And is the problem with Firefox only? (Just making sure...)
Just a couple of thoughts here:
Firefox had a sound issue on the older versions of Flash.. Generally, then newest Flash 10 should fix it.. So...If you don't have the latest version of Flash or Java, please follow the instructions below to get them:
Please install the latest Flash and Java using the instructions below:
Uninstall your current Flash from Add/Remove Programs, then download the full Flash uninstaller from the link below:
Once that's done, uninstall Flash by using the Flash Uninstaller at the link below..
After that's done, then download the manual Flash player installer from the link below.. Download it to your desktop and Run it to install the newest Flash for Internet Explorer.
Once that's done, if you're also using Firefox, visit the site below while in Firefox, then download and run the Flash plugin installer.
Click on the link to Sun's Java below, then scroll down and click on the "Java Platform, Standard Edition" section, next to "JDK 6 Update 20 (JDK or JRE)" and click on the "Download JRE" download button. At the next page, select the Windows platform, make sure the "Language" is correct, accept the license agreement, then click on the "Continue" button. Next, download the full ''Windows OFFLINE Installation'' file to your desktop,(about 15 MB), scan it with your antivirus (just to be sure it's clean). Once that's done, if you've already got a Sun Java version on the computer, open the Control Panel, double click on the ''Add/Remove Programs'' section, then uninstall all previous versions of the J2SE Java listed there. Once that's done, then install Java JRE 6u20 from the downloaded installer.
Hope this helps.