Our company installed an unfinished 3,4,and 5 inch resawn old growth hickory floor in about 6000 ft. on 2 levels.The flooring in the middle level(above grade with a finished basement) pops and cracks in several areas.The contractor tried screws in some places with no success and in some areas that will be hidden(under floor to ceiling cabinets in master closet) a large amount of 2 inch screws were installed with little success in getting rid of squeaks.The floor is 25/32 OSB.I have some experience in installing with more experience in sales but have run out of ideas.The heat or air have not been turned on yet and I am worried that they might get worse after heat is turned on. I have seen more problems with pops and sqeaks since OSB has become more popular.Any ideas before we start sanding?

The noises MAY be coming from the subfloor system rather than the hickory flooring. I say that because refastening the hickory flooring had no effect. IF the noises cannot be eliminated by refastening, then perhaps removing a few boards in the location of the noise will aid in determining exactly what is causing the noise. If one removes a few boards and the noise is stopped, then you could assume that the hickory flooring was creaking. That could be due to many things; broken or split T&G's, poor nailing, bad milling, uneven subfloors, etc. Another issue you have in front of you is failure to acclimate the flooring to normal living conditions prior to having it installed. It would be wise to wait a couple of weeks MINIMUM after the HVAC is turned on to start sanding the floors. I think you still may get some shrinkage. IMO, 5" planks should be glued as well as nailed. And possibly 4" as well.

wide plank hickory is not the most stable specie out there. How long after the flor o went down were the squeeks noticed? That stuff will shrink and swell fast and furiously in an uncontrolled enviroment. Check the moisture make sure its not picking any up. Hopefully someone checked it before it went down to give you a baseline.