There used to be a magnet on my refrigerator that said “Boiling Water” and then had detailed instructions for how to boil water. You ask a silly question, you get a silly answer
I don’t just answer questions, I offer solutions.
Even better than Tupperware. 
Peace,
mangeorge
Heck, I guess you gotta plug in “ice cube tray”.
This sounds like iceberg ice. A few years ago I remember seeing an article about someone flying in iceberg (or glacier?) ice to Japan because it was a current fad. As it melts it supposedly makes pinging and crackling sound as tiny high-pressure gas bubbles are released. Sort of like “pop rocks”, but with ice and air rather than hard sugar and carbon dioxide.
I wonder if someone in Japan made a “high pressure” ice machine which creates arificial iceberg ice?
And about the OP, maybe the top surface of the water needs to cool fast for some reason (and the lower tray would see some room-temp water right above it, and cool slowly. Try placing something between the trays? I wonder what THREE trays would do, if the middle tray was left empty.
i don’t think there was an iceberg involved. this man made rectangular “logs” of ice, that when sliced sounded like crystal glasses being played. when placed in a glass and a beverage poured, the ice would produce various tones. like a song in your glass.
the iceman was one of the national treasures of japan. i believe that he sold his ice in kyoto.
…now if I could only figure out what to add to this package of powdered water…
Faerie’s breath, of course.
Peace,
mangeorge
Are these trays designed to stack? Are they naturally spaced out?
If not, I suggest trying to raise the top one slightly. Exactly why, I leave to the Perfect Master.
The tupperware ice cube tray is pretty righteous but then again I am a complete kitchen gadget slut. The sluttiest. I don’t know which is worse, the Calphalon, the Braun hand blender or the goddamn potato ricer.
But Tupperware is sooo last week, Padeye.
And I’ll match you gadget for gadget any day. Betcha don’t got a Whirlypop.
mangeorge
Okay, spill. What’s a Whirlypop.
Oh, and I just ordered metal icecube trays for my dad from that site. Thanks!
I’ve seen this problem, and my WAG is that it’s actually related to how long the ice has been frozen–the lower one is harder to get out because it’s been in there for a day or two longer. So, whenever I fill a new tray, I put it in at the bottom of the stack so the trays are being constantly rotated out. Also, this prevents water from the new tray from dripping into the previously-frozen ones.
whirlypop
I got mine at Bed Bath and Beyond for 25 bucks.