In the past I have had the same problem due to a bad ground on the CB and it was grounding out through the antenna.
I the same problem again now garbled sending. As per our club radio expert, my antenna is fine, my mic is fine, my radio is toast. They are cheaper to by a new one than to try to have it fixed. Time for a new CB for me. Borrow someone else's mic and see if that works. It will tell you if it is the problem or not.