Why Distorted audio on transmit is often caused by RF feedback: some of your own transmitted signal is picked up by the microphone cable and coupled back into the audio stages, where it gets rectified and re-modulated. A clip-on ferrite bead or several turns of cable through a ferrite core raises the impedance to common-mode RF current on the outside of the cable without affecting the audio inside it, so the stray RF never gets back to the mic input. Other cures for the same problem are better station grounding, moving the antenna farther from the operating position, and reducing power.
Watch out Adding feedline does not lower SWR, it just adds loss that masks the reading at the radio, and the squelch control only affects the receiver, not your transmitted audio.
Distorted audio on transmit = your own RF sneaking back in. Ferrite on the mic cable chokes it off.