Are you sure it's the coil?
Hearing the spark jump from the rotor to the contacts in the distributor is real common.
I run these on my own car before I ship them and I hear the spark in the distributor.
If you are sure it's coming from the coil, chk the coil body to the bracket tightness. (While the car is running hold the coil body)
Sometimes the coil is a little loose on the bracket, and it may be vibrating from the magnetism.
Insert a small piece of rubber between the coil body and the bracket if that is what it is.