First, did you install Impulse, and update your game? If no, that is probably the problem. What's more, there were many more gameplay enhancements (positive) that were made since the original popular version. If you still have this problem, I would suspect a sound driver or graphics issue. Also, sometimes reinstalling the game fixes bad install issues (uninstall first).
Personally I highly recommend you upgrade to Twilight of Arnor. It may fix your problem. Even better, upgrade to Dark Avatar first, I thoroughly enjoyed both the campaign and the free-style games (metaverse or not) of all three iterations; but now I would never go back to DL or DA (the TA is deeper in strategy and has more stuff). So enjoy DL thoroughly before you enjoy DA thoroughly before you enjoy TA thoroughly! Each upgrade changes the strategies a bit, particularly giving you other options to go about winning.
