Sorry, I stand corrected. I had assumed since the data sheet lists the compressor as 2 speed... that it in fact was 2 speed. But it's dual capacity by using a port to either reduce the compression or bypass refrigerant (not sure which since as a "mere mortal"...not a HVAC god I don't have access to the details of the unit design... Trane doesn't publish it's P&ID's) and the electrical drawing in the data sheet wasn't clear how the capacity change was accomplished. I suppose you could use a 2 speed motor... but it's much cheaper to use a valve... and the next step is price is to use 2 compressors. VFD's haven't yet been implemented in the mainstream residential product offerings.
So from a standpoint of noise, the condesor fan runns a little faster, but the compressor runs at the same speed, althouhg loaded more.