I know much simpler way:
for (int index=0; index<repetitions; ++index)
{
System.Console.Beep(800, 250);
System.Console.Beep(970, 250);
}
Notes:
You did not explain the profile of frequency modulation; this is one of the simplest variants.
You may want to run it in a separate thread — it will work.
You don't need to make you application a console application. This code will run in any application.
—SA