Dan,
If what you describe as a 'warbling' audio is what I
think it is, it isn't the antenna that's a problem, but
the power supply. Sounds like you're running the power
supply beyond it's capabilities. Drawing too much
current, the voltage 'sags', and causes a 'warbling'
audio, no matter which radio you use (unless both radios
have exactly the same 'problem', which is unlikely). I
guess it's possible, but antennas have very little affect
on transmitter audio.
'Doc