I noticed today that my bottom bracket, crank, chainring, chain, cog or rear hub is making a grinding-crunchy sound when I back pressure as I'm slowing down. If I just use brakes, and slow down then there is no noise and the drive train runs smooth as silk.

So I'm assuming its somewhere in the engagement of the chainring/chain.

There is play in the chain, but not that much, maybe 2" on the bottom. The top play is less than 1/4" an inch. By comparison my wife's Fuji Betsy (traditional track dropouts) has about an inch of play on the top and 2-2 1/2" of play on the bottom.

Chain alignment looks good between the rear cog and chainring, but I did notice my chainring is just a little - like 1/16th to 1/32nd of an inch narrower than the chain linkage per tooth. Its just over halfway basically. On the rear cog, the chain-to-tooth fit is exact.