Severe floor creek-18LT

[LA48340]

In the floor space in front of our vanity/toilet/shower we have a very creaky floor.
I got under the unit and it appears to be the area right above the tanks. I was going to try and squeeze some Loctite adhesive in the gap between the floor and stringers but its not accessible. If the lip of the stringer can be located...would driving some long self tapping countersunk screws through the floor into the stringer flange be a solution. Its very annoying and wife is complaining. thanks.