I have an SM99 from a very old church. In the winter it gets cold in there and the mic makes a crackling noise when it is spoken into, but it only happens when it is cold in there. I have replaced the cable, but I do not have another mic to try. Any suggestions would be greatly appreciated.
The problem could be static electricity. When it is cold, the heat is on and the air dries up. A person walks up to the microphone on carpet(?), builds up a charge on his body, and the charge is discharged through the microphone because the mic's metal body is grounded via the mic cable.
A wireless mic would not have this problem as it is not grounded.
A foam windscreen placed over the SM99 grill might help stop the static from discharging through the mic, though touching the mic will still cause a discharge.
You can also try an anti-static mat placed on the floor near the mic that will discharge the static when a person stands on it.
If the mic were defective, it would act up all the time, not just in cold weather.