Typek na KVR foru resil problem se slabym, ale slysitelnym bzucenim pri ovladani Forte externim kontrolerem (Linnstrument) - ukazka.
Nakonec psal na support Kurzweilu a dostal tuhle odpoved:
While I cannot comment on future product plans I can confirm that there is an audible noise (all be it very low level) induced when triggering the Forte via MIDI DIN IN. This appears to be due to the proximity of certain internal components to the A out DACs (predominantly the right channel) post the MIDI port optoisolator. This went unnoticed by all (up till now, thanks for the report) largely due to the low level and how much gain is thus required to make this audible to a noticeable degree.
So the good news is your unit is physically fine/normal. The downside is this is normal - but hopefully low enough level that it does not impede typical work conditions. The alternatives (which I think you too found) are to either use the USB MIDI functionality instead (if possible) and/or route the audio to the B outs which do not appear effected (the Global mirroring mode for Out Pair B makes this a one switch fix - manual ref. pg 12-5).