I’ve found an issue that creates additional very low (probably C0 or lower) note playback when I copy notes from one staff to another. For example, using clear trumpet and copying notes from one measure to the same measure in another part (say from Trumpet 1 to Trumpet 2,3, and 4) I invariably get stray notes at the bottom of the MIDI range. These new notes don’t appear on the piano roll editor, but are quite audible upon playback. I’ve not had the same issue with the “noisy” sax instruments or trombones. I did have the problem occur with an acoustic bass instrument, though (GM Acoustic Bass).
Are they keyswitches?
As Derrek suspects, they are most likely key switches. If you’re using GM sounds you will hear those. You don’t see them in the pianoroll because they are generated on the fly. What you must do is click on the little cog wheel beside your VST or MIDI Instrument in PLAY mode. In the boxes beside the midi channels make sure DEFAULT is chosen.
The trumpet patch I was using was not a GM patch. I was using “clear tone exp” which appears to be a Halion instrument. All slots in the MIDI rack are set at default. Since when do GM instruments use keyswitches?
Ok, it’s not a GM patch, but it’s a full range patch, meaning that you would hear low range key switch notes if the wrong expression map (i.e. one for the default trumpet) was in effect. Since the default XMap is not using key switches this can’t be your problem. Maybe another explaination pops up 
Click the little cog button next to the instance of HALion Sonic SE in the VST Instruments rack in Play mode to see which expression maps are assigned. I would be willing to bet that the channel in which you’ve got your trumpet patch loaded it’s using the ‘Trumpets Combi’ expression map.