strange knocking felt in shifter
 

Hi everyone,
First, some info in my car: 1992 Mustang GT with a T5 transmission and 43,000 miles on the odometer. I recently noticed a slight knocking in my shifter (Hurst comp. plus) when it is in the neutral position with the clutch pedal released. If I press the clutch pedal to the floor, the knocking decreases. With the knock I can hear a tapping sound coming from the tranny and the shifter feels like there's someone tapping on a shift fork with a hammer (best way I can describe it). The knocking is at random intervals as if something is bouncing around in the tranny or clutch (it is not a constant tapping). Any ideas what this could be?