I fixed a lot of squeeky spots in a floor a few yrs ago for a friend.
The main culprit is/was nails meant to secure the floor planks that were not securely nailed into the floor rrafters.
The nails were just barely into the rafters and then shooting out the side of the rafter.
The nails weren't really holding the planks secure. So the flooring over time has a chance to buckle a very small amt as wood does naturally from humidity.
Not being secure, the planks are loose a very tiny amt from the rafter and every time you step on those spots, you hear the nail(s) being pushed into the wood of the rafter and then being pulled back out again as the plank returns to it's slightly unsecure/flat condition.
I was able to simply see most of the offending nails that were sticking out the side of a rafter in the basement near the the top of them.
A vise grip was very handy to pull the nail completely out of the wood, plank and rafter.
The planking above is still not secured tight/down on the rafter as it isn't nailed down, but it never was anyway, thus the squeeking noises.
But w/o the nail(s) in place,,the squeeks are gone.
A couple of especially bad places where the planking was bowed upwards, we used one of the 'puller' fixtures to draw the plank back down onto the rafter.
A simple plate that screws into the plank right next to the rafter, a threaded rod w/J hook afair hooks under the rafter and the plank is pulled down into place.
I understand you can't get at all of the noise makers as some are sealed inside the attached garage roof. But some might be abel to be quieted in the basement area.
An assistant lightly jumping/bouncing on the floor above helps find the offending nails and sometimes they are the cross braces betw the rafters as well making the noises.
They are simply nailed into place and wood to wood contact, dry as it is many times is the source of the racket.
You can actually see the movement when that is done above you.