I am running Platinum (2017.01) but have seen this in previous versions as well...
 
Sometimes when a clip is dragged (or directly change start time) the sound of the clip is altered.  It sounds like the clip is 'ducking'.
 
There is no overlapping clip.  Either I drag into blank space or a space voided by deleting another clip.
 
If I restore the clip to its original position it sounds normal again.
 
It does not happen all the time (even within the same track) so I was ruling out signal flow through busses, etc.
 
Any thoughts on why this occurs?
 
Thanks!
-Dennis
 

Ducking is usually taken to mean that an audio signal power is reduced when another signal is added or increased. If you are saying that the moved signal sounds less loud when moved to a position in which other sounds are present, you may just be experiencing a psychoacoustic phenomenon known as masking. The auditory apparatus and the brain perceive a given sound as less loud when other sounds are present. Put a meter on the solo track and see if there is really a drop in amplitude. If you are saying that the clip is less loud without other audio being present, then it is odd to describe that phenomenon as "ducking."
 
Masking does not just affect perceived loudness, but can affect pitch and timber perception as well. In addition, the physical phenomenon of destructive interference can reduce the actual sound pressure level when other sound is present, and by affecting different frequencies which in turn are perceived as different loudness along the Fletcher-Munson curves, can affect loudness, pitch and timbre. 
 
Short answer, changes in the sound of a clip are to be expected if the clip is moved relative to other audio. How much change should be expected is too complex to predict. 
 
 

"...no overlapping clip..." I assume you mean on the same track?
 
If you have clips in OTHER tracks playing at the same time,
and you have a common compressor/limiter on them,
you will experience 'ducking'.

Ok...  tried to do a bit more isolated testing to see what is what.
 
To clarify, I am working with a single track and there is no other audio playing on other tracks. There are no muted clips that I am dragging over.   I simply drag the clip (or change its start time) to a new/open position... 
 
Also to clarify, I wasn't saying that the clip was 'ducking'.  I merely stated that it sounded like that ...
 
This is very repeatable with various clips that are split from the track at different points in time.  It has also happened within different projects over different periods of time.  Not simply one track in one song...
 
Odd thing is that once the clip has been moved and exhibits the 'masking' I simply move the clip again by one (1) tick and the full/normal sound returns.   If I move the same clip again the 'masking' returns.  Move it 1 tick and normal sound is restored...  rinse, repeat as often as you'd like.  It happens over and over...
 
Not expecting any answer or solution here at this point.  Just sharing to let others know if should happen to them.
 
Thanks,
-Dennis
 

Zoom time way in to see if there is a fade at the beginning of the clip both before and after the move(s)