Your dll.xml file should contain two 757 related entries.
[code]      <Launch.Addon>
           <Name>Captain Sim Menu</Name>
           <Disabled>False</Disabled>
           <Path>Captain_Sim\Captain_Sim.b757.menu.dll</Path>
     </Launch.Addon>
     <Launch.Addon>
           <Name>Captain Sim 757 Sound</Name>
           <Disabled>False</Disabled>
           <Path>Captain_Sim\757\cs.sound.dll</Path>
     </Launch.Addon>[/code]
As you see, one is the cs.sound.dll and if it's missing and therefore doesn't get loaded, you will miss the sounds.
So maybe check the dll.xml file if it was altered with the installation of 4.5. If not, some missing rights may have prevented this step.
Please also check if the cs.sound.dll is in that Captain_Sim folder.