Norris - I've been in Arlp a long time - on the (fake) level II - one can see huge buy/sell orders often 1k shares and even more sometimes (2, 4k) (big boys) Because it's often in the news (coal stocks) Motley Fool et al, traders pile in (even if for a few ticks) and get out fast. They love the "div" (I know units) stocks as others rush in for that on the news while they exit...
As others mention some took profits prior to news.
The market maker as well seems often to be "picking his nose" (just stalls and you can see him walk the pps down).
So, no worry if longer term investor and great if trader but follow where the money flow is going.
Just a guess: ARLP's unit price has gone up quite a lot over the past week or so. Probably someone wants to take a quick profit rather than risk losing their windfall if the quarterly report should disappoint.
Not that I expect any problems with the report. I bought quite a few units today to take advantage of the temporarily cheap price.