Topic "engineered hardwood wide plank (7 1/2") - staple" a message from ullsign

Hello everyone,
I have a engineered hardwood wide plank (7 1/2) installation in progress. I have installed about 200 - 300 SqFt from aprox 2000 SqFt, with 1 1/2" 18 G narrow crown staples over 5/8" plywood. Soon (h's) the floor start crackling and popping as i walk over. The nail schedule it's ok between 3 - 5". The sub-floor is stable with very minor movement (its a wood structure, new home). I have tried in a separate section with couple (6 long plank) of boards nailed down using 1 3/4" 18 g cleats and I having same crackling popping issue. Humidity in the floor, air are ok (47% @ 22C air), hardwood left for 72h acclimatization. We had the rep on the site and they conclusion for the crackling and popping is the very minor movement of sub-floor (can't be noticeable or anyway it's less then 1-2 mm over 3') and inproperer nailing down.
Contractor want us to try using sub floor spot glue under the hardwood on every 3 - 4 plank. Using spot glue under hardwood is that ok? As i know for sure will void the warranty. Any help on this truly appreciate. I can provide more technical info from installation upon requested.

Thanks
edited by ullsign on 5/30/2014