If you suspect your toilet is leaking, but aren't sure where, add some food coloring to the water in the tank. If you see colored water inside the toilet bowl, suspect a defective flapper that needs to be adjusted or replaced. If it shows outside the toilet near the back, suspect a faulty tank-bowl gasket. If you see any water on the floor near the base, check for a faulty wax ring.
There’s more to soundproofing than just insulation. “Blocking” noise with a non-hardening caulk to close off airborne sound paths. “Breaking” the sound path using resilient wood studs with metal clips. Last, isolating and eliminating “vibration” with special acoustical matting that seperates the wall structure from floor vibrations. You can get all these items in soundproofing kits for both interior and exterior residential walls. Besides blocking most noise transmission, one obvious benefit is better energy efficiency, with greater “r” values.