Most likely cause is that your clock is out of beat, ie, the tick is uneven. If you set the pendulum swinging then gently move the bottom of the case to one side then the other you should hear the change in the tick. Stop when you reach the point where the tick and the tock sound to be even. This should cure it.
If this doesn't work, check that the hands are not fouling one another, and that they are not scraping the dial or the glass.
If neither of these work, I suspect that your clock needs to be looked at by a professional
Gordon, December 2005
