It depends on the reasons that the edges are sticking up. You need to assess if there was a moisture problem creating edge swell, or if the ply was installed too close together with no expansion gaps in between, or if the joists under the ply aren't level. There isn't a one size fits all solution. In no cases would you "hammer it down". That would damage the plywood.

Oh my gosh, I hope it's because the ply was installed too close together. I can see expansion gaps with ply being flat, but some expansion gaps not being flat, it's just kind of a mix.

If it's the joists or a moisture problem, that seems to spell trouble. It's very random though, not near any water source just a few places. The house was built in '76 if that makes any difference. I see water marks near the sliding glass door and the fireplace, but no uneven floors. I can see I'm going to have way too much time looking at these plywood floors before the install.

Are the floors generally flat and just the edges sticking up?

People mentioning moisture problems are just being careful. Not to say its not a concern but unless you had flooding in the. Past it probably isnt an issue. Giving the subfloor weeks to breath before installing will be good. But a moisture meter can tell you straight up if you have issues.

I wouldnt "nail" the subfloor. Spend an evening rescrewing the subfloor down to the joists. Check for spongy spots. Suggest you spend that extra hour doing the work. You will be glad in the future you did.

cblanco75- Yes, I believe it's just the edges. One edge might be up and then it's flat all around.

Greg-These floors are nailed down, not screwed. Interesting! We had someone look at our deck too which is nailed and he told us that now days everything is screwed and bolted. That makes much more sense.

So when the installer comes in, what do you think he will do?

When the installer arrives you will escort him around and point out the high spots. In fact mark them clearly prior to his arrival. I just had 400 sq ft of WO installed tying in from new floor to old. There was a high spot at one corner and I asked the installer to bring out his sander to level the floor. First we made sure the sub-floor was properly screwed down.

Something to consider. Wood never stops moving. It responds to the environment it is in. I would never install hardwood that hadn't been sitting in the space it is going to be installed for at least a couple weeks to become acclimated to the environment it is going to be in. You want the new wood to be friendly with the old. Mine was stacked in the living room for 4weeks. We had to do a do-see-do with the wood every time we went thru there. Pain in the neck, but the floor looks great. Hickory is great wood. Good luck with it.

Over time the nails come loose from the movement. Screws do a better job keeping things fastened and will help prevent creaking.
Are you are going to do the subfloor work or your installer?

A couple boxes of 3 in screws and a drill is all you need. Maybe 50 bucks for the screws. But just rescrew everything then you can see where the natural high and low spots are at and then you can have the installer sand a seam or shim an area as necessary.

Ok thanks Greg. That sounds easy enough even for a couple of non-DIY'rs like ourselves.