Thats what I've had also.
Are you using the smbios.plist form "iMac12,1 / Core i 1155"?
Well in that case don't. Try the smbios.plist from:
http://Olarila.com/forum/viewtopic.php?f=17&t=134
MacPro3,1 / Core2Quad 775
The iMac smbios.plist gives you power savings on your audio, just like a MacBook.
Thats what you hear when poping.
Just replace the smbios.plist and use the one from MacPro3,1 and enjoy your sound again
The smbios.plist from MacPro3,1 don't have power savings for audio.
And uninstall "antipop". In the folder you'll find an uninstaller.
Greetz, René