Thanks everyone. After RB's reply suggesting my problem may not really be air bubbles I rethought the likelihood I have dust. I looked over recent negatives and noticed what could be a water course down the same latitude on all the frames, and wondered then if dust embedded over that trickle of water dripping down the weighted-down negs. I have seen a similar phenomenon lately-- a bunch of frames with dust in a similar pattern running from side to side of the frame, which would be hanging vertically when the negs were drying of course. So I will try an experiment to cover the shower stall with plastic (dust free!) after I humidify the stall. If this fails, I will move on to do a test with another brand of BW film versus APX. Other than particles in the developer/fixer, it is either dust or bad film.
I have noticed on occassion some of my APX develops with smeared areas, as if either the emulsion has gone haywire or perhaps the developer was weak and did not fully develop little areas of the film. I have seen this effect on maybe 5 of the past 30 rolls, and in one case identified spent developer as the problem. But in this present case, the HC110 was fresh mixed, and as I say, gave me really nice looking frames, other than these white dusty-looking thingamabobbies.
Appreciate the help. Thanks. rolly