No volume with some YouTube videos in Mountain Lion

Question

I've installed Mountain Lion and the latest Flash player and find that certain YouTube videos (some, not all) play without any volume, completely silent.  A full reboot didn't help.  Here are a couple of examples that videos without volume:
http://www.youtube.com/watch?v=NXUPDAMc_6o
http://www.youtube.com/watch?v=YLO7tCdBVrA
Some, not all.  This one works fine:
http://www.youtube.com/watch?v=hXyGSfO7TiQ
Are others experiencing this?  Any solutions yet? 

Answer 1

Hardware:
    Hardware Overview:
      Model Name: MacBook Pro
      Model Identifier: MacBookPro8,1
      Processor Name: Intel Core i7
      Processor Speed: 2.8 GHz
      Number of Processors: 1
      Total Number of Cores: 2
      L2 Cache (per Core): 256 KB
      L3 Cache: 4 MB
      Memory: 8 GB
      Boot ROM Version: MBP81.0047.B27
      SMC Version (system): 1.68f98
      Sudden Motion Sensor:
          State: Enabled
Startup Items:
    HP Trap Monitor:
      Description: HP Trap Monitor
      Location: /Library/StartupItems/HP Trap Monitor
      Provides: HP Trap Monitor
      Enabled: Yes
      Uses: HP IO
      Order Preference: Late
    MySQLCOM:
      Description: MySQL 5.1.40-community
      Location: /Library/StartupItems/MySQLCOM
      Provides: MySQL
      Enabled: Yes
      Uses: Network, Resolver
      Order Preference: None
    ProTec6:
      Description: Nalpeiron Copy Protection 6
      Location: /Library/StartupItems/ProTec6
      Provides: Nalpeiron Copy Protection 6
      Enabled: Yes
      Order Preference: Early
    Qmaster:
      Description: Qmaster services
      Location: /Library/StartupItems/Qmaster
      Provides: Qmaster
      Enabled: Yes
      Requires: Disks, Resolver, Network
      Order Preference: Late
Software:
    System Software Overview:
      System Version: OS X 10.8 (12A269)
      Kernel Version: Darwin 12.0.0
      Time since boot: 32 minutes
Kernel Extensions:
System Launch Daemons:
          [not loaded]            bootps.plist
          [not loaded]            com.danga.memcached.plist
          [loaded]                com.vix.cron.plist
          [not loaded]            exec.plist
          [not loaded]            finger.plist
  [not loaded]            ftp.plist
          [not loaded]            login.plist
          [not loaded]            ntalk.plist
          [running]               org.apache.httpd.plist
          [not loaded]            org.cups.cups-lpd.plist
          [loaded]                org.cups.cupsd.plist
          [not loaded]            org.freeradius.radiusd.plist
          [not loaded]            org.isc.named.plist
          [not loaded]            org.net-snmp.snmpd.plist
          [running]               org.ntp.ntpd.plist
          [not loaded]            org.openldap.slapd.plist
          [loaded]                org.postfix.master.plist
          [not loaded]            org.postgresql.postgres_alt.plist
          [not loaded]            shell.plist
  [not loaded]            ssh.plist
          [not loaded]            telnet.plist
          [not loaded]            tftp.plist
System Launch Agents:
          [loaded]                org.openbsd.ssh-agent.plist
Launch Daemons:
          [loaded]                com.adobe.fpsaud.plist
          [loaded]                com.google.keystone.daemon.plist
Launch Agents:
          [loaded]                com.google.keystone.agent.plist
          [loaded]                com.hp.help.tocgenerator.plist
          [running]               com.SimpleTech.ButtonPoller.plist
User Launch Agents:
          [loaded]                com.adobe.ARM.202f4087f2bbde52e3ac2df389f53a4f123223c9cc56a8fd83a6f7ae.plist
          [loaded]                com.iLike.Agent.plist
          [loaded]                com.valvesoftware.steamclean.plist
          [loaded]                com.veoh.webplayer.startup.plist
          [loaded]                net.sourceforge.tvshows.plist
User Login Items:
          AirPort Base Station Agent, iTunesHelper, AdobeResourceSynchronizer, Dropbox, Popup