Floor noise tongue groove

Are the joist 16" oc? If not you may want to sister them for added strength, and give you a better nailng/screwing surface. The 1/4" doesn't give the best support for subflorring, so you need to upgrade to 3/4" or at least 1/2" plywood. It's also a good idea to use a glue like liquid nails or other adhesive over the joist. Your fastners should be placed about every 8 inches. Good Luck!

I'm guessing that any screws that hit the T&G could then be seen from the main floor room if too long - the issue with "too long" is that anything that is just long enough to not show won't do much good, and guessing this is being used for living space.

wood on wood is an issue - needs a barrier between or this will happen no matter what you do. Wood expands and contracts with temp and moisture - impossible thing to stop and over time loosens fasteners.

If the weight isn't an issue, would recommend a heavier sub-floor with some sort of barrier between the surfaces; some have used roofing felt with reasonable success but there are products specifically for this application. There are 3/4 or 1" T&G sheet goods that provide a very good base over your T&G pine. Check your local home center; they come in 4x8 sheets.

And of course, fasten to the joists and not just to the T&G pine for the connection strength.

If that isn't an option, then laying a lighter sub-floor in the opposite orientation to your current flooring. Adhesive may help, but 3/4 pine isn't much to support the weight of persons and furniture without movement. alternating will help.

For a "quick fix", try to remove the most offensive area, apply the adhesive, and attach replacement sub-floor -- BUT, remember, wood moves and a solid mechanical connection, while sounds like the answer, may not be to your best advantage, so add the barrier (and ya, that changes the height, and ha, then that ... so much for quick, right) :)

Just my 2 cents;

The T&G is 2" x 6" x 8' pine. Because they are the ceiling of the room beneath. I can not add any new joists. Here is the conclusion I have come to. 1. Remove all the old particle board subfloor. 2. Place a bead of liquid nails in any of the T&G joints that have a gap. 3. Use new ¼ plywood 4'x8' sheets run the grain of the plywood across the 2x6 T&G pine. 4. Use Titebond   II 1-gal. Premium Wood Glue. This gives me 60 minutes to set up. Cove the T&G is 2" x 6" x 8' pine then place the plywood on top. 5. Mark the joint locations on the plywood. The drive 1 1/5" deck screws every 8" on either side of the joints. (A lot of screws) 6. Place a layer of QEP   2 ft. x 3 ft. x 1/4 in. Cork Underlayment Sheet. On top of the plywood. 7. The padding and carpet. If it makes noise after all this so be it! The only other solution is to sell the house and that will not happen. Thanks for all your help.