The floors are about 12 years old but were completely refinished about 6 months ago. There was always a bit of noise and in certain areas it seems like the sub-floor might be the problem. But over the past few months it seems like we are having problems in a lot of areas ad it sounds like it's the hardwood not the sub-floor. Some of the sub-floor issues seem to be where duct work passes under it. Any thoughts on what could be causing the cracking noise and what I can do about it.?

racking and popping can be normal in season al chnages...I suspect the floor may have been undernailed and
with the mild winter and high humidity as of late) at least here in northeast)..the floors may be ging a little crazy..

would need to hear or see to really make a good determination....

you can try accessing floors from underneath and securing with shims in the joist to fix any subfloor issues and then send screws up into the floor from under to try and cecure some of the cracking..

Thanks for the suggestions.

I do have access from below and will give it a try. The problems are widespread so i was hoping to avoid having to identify and fix every individual spot. But i guess there's not "magic" cure... it seemed curious to me that the problems seemed to become more acute after the floors were sanded and refinished last fall and I wondered whether that had led to the problem.

how thick are the floors?

The finished floor is 3/4 oak. sub-floor is 5/8 OSB.

Since you had noise before then had the floor sanded and finished I would say it is the new finish breaking away from each board. Unless sub floor is secured better the noise will just eventually return to the way it was. Might be worse if they didn't use sealer coat so you are getting sidebonding.

Side bonding can be a good theory, but only if waterbase finish was used..

I tend to think it has more to do with current climates, mild winters...high humidity....I uess your area may be important to know...

eitherway...as mentioned..not like it will be getting worse..most creaking and squeaking comes form your subfloor..