Want to fix it right and once and for all?
If you want it right get rid of the 1/2 and use 3/4" Advantec T X G. Constrution adhesive on the joist and ring shank nails of ceramic coated deck screws to attach it to the joist.
The old subfloor can be cut out with a Tow Kick saw and an ossilating saw or sawsall.
That 1/2" subfloor in not doing you any favors.
If you want it right get rid of the 1/2 and use 3/4" Advantec T X G. Constrution adhesive on the joist and ring shank nails of ceramic coated deck screws to attach it to the joist.
The old subfloor can be cut out with a Tow Kick saw and an ossilating saw or sawsall.
That 1/2" subfloor in not doing you any favors.