Unexpected Tremolo or Vibrato effect

[equant]

I've created a soundfont using Polyphone from samples taken from a casio keyboard. The soundfont has 4 instruments, that each use 4 samples. For each sample I've created loop points. In Polyphone, when I play the soundfont instruments, it sounds just like playing the keyboard. However, when I open it with fluidsynth, there is a pulsing rhythmic quality. I would call it vibrato, but maybe it's tremolo? I might not know the difference. It seems to happen on all of the sounds and even other soundfont files. Is there a way to turn it off? I've tried setting CC 1 on midi channel 1 to 0, but there's no change in the sound.

[equant]

I tried the soundfont through timidity, and it sounded correct (no vibrato), so this appears to be something that fluidsynth is doing that I'm not understanding how to disable.