Flashforge Adventurer 3 Filament feeder loud thumping noise, not enough filament extruded
Advice from another source suggested thoroughly cleaning the feed gear on the bowden extruder.  When I looked closely there were plastic flakes all over the mechanism.  I used compressed air and a brush to clean it. 
I also discovered expert mode in the FlashPrint software, which enabled me to slow down the speed at which fill is laid down.
Now I have good printing results with any filament.

EDIT AND UPDATE::
I have continued to have problems with PLA.  For most of the last year I printed using ABS with no similar problems.  I guess that PLA is simply rougher, scratchier than ABS and catches in the tube.  I found a comment that putting olive oil on the filament fixes it.  I used Vaseline.  Things were fine for a while, but a retailer said this would lead to other problems.

So far, no permanent answer to this question.