[Yaesu] re warble audio on FT-1000D

[Fern]

    I've a friend who just emailed me to say that his prized FT-1000D has 
just developed a problem with warbly sounding receiving audio. I'm thinking 
that it may sound just as bad on transmit mode but don't know that at this 
point. Where should one look for the culprit problem and what the fix may 
be? To me it sounds like this may be a synthesizer problem but I've never 
had that problem with my own FT-1000D. I did a gooble on that but came out 
empty handed. Any and all comments are appreciated with this.
Thanks from Fern   VE7GZ