Nonrunning clock strikesthe three quarters of an hour

Yesterday at our store I had an unusual experience. It could have a perfectly logical explaination.In my workroom I have a four foot tall Howard Miller pendulum clock. I have it sitting on my desk as I had been working on it. It runs great but only for about 9 hours at a time. It is quite loud with the deep sounds of the Westminister chimes and strikes a deep tone on the hour. The chimes occur on the quarter hour. I haven't worked on this clock in over a month nor has it been wound during that time. In fact so many minor projects are stacked in front of the clock, I couldn't even get to it to wind it. Yesterday I was standing well away from this clock when it struck the three quarter hour. There is no mistaking that clocks chimes. I have no explaination for it. A better clock repairman than I may be able to explain it. But that clock hadn't been wound for well over a month and the pendulum was very stationary.