Windows 7 - Control Panel - device manager - sound section
If there is lots of High Definition Sound Device, remove all these except the last one.
Your sound in windows will still be working, and now GM only takes 3 seconds to load a game (ex: empty only one room). Before these you had to wait 7 seconds minimum.
But when you reboot windows, all the drivers will be auto installed again. So repeat the process...
It works for me.
Found a slightly easier, though still temporary, solution to this problem that does not involve opening up the device manager and messing around with things
For those of you like me, who are running GM8 in windows 7 on a laptop or PC, and are having problems with loading games, head down to the 'Volume Control' Icon in the bottom-right hand side of the screen and right-click it.
Click on playback devices.
Right-click the 'Realtek Digital Output' and 'Speakers' icons, and press disable. Make sure you have 'Show Disabled Devices' enabled, so that you can see them when you need them enabled again!
These settings will stay put every time you boot up the PC too!