1) Difficult to guess without knowing exactly what you are doing and what is the patch you use when you hear that.
Try setting KSyn=0 in for all LFO.
If the effect disappear what you hear is the fact that the LFO are global for all notes.
This is how it works for the moment...
2) PreenFM won't play more notes than what says "Voic" in the engine 1st page.
Any new notes stop the older ones.
3) Not sure i get it.
What you hear when modifying the enveloppe is totally different if you modify a enveloppe from a carrier operator or a modulator operator.
Carrier will modify the volume of the sound... like it does in substractive synthesis.
Modulator will modify the spectral of the sound.
This is the same with oscillator.
Look at the PreenFM algorithm schema.... A carrier is any operator at the bottomo of each alg. The modulators are operator upper.
Experiment with simple FM synthesis.
Set IM2 and IM3 to 0.
Set IM1 to 4.0
And start modifying enveloppe 1 and 2 and oscillator 1 and 2.
When experimenting with other algo the algo paper you get with your kit is your friend ;-)http://www.preenfm.net/manual/algorithms