I think there is merit to some of the suspicions about the usefulness of sound in health, but people's ignorance, wishful and magical thinking, and flights of fancy result in any legitimate information getting bogged down in a sea of perpetuated crackpottery.
Consider many of the things that we presently do for health:
various minor surgical procedures
Tai Chi practices of tapping and bouncing
All of these involve the intercession of a third party or a tool to enhance the effectiveness of self-care.
Various authors have put forth theories on aging and disease resulting from the accumulation of crud and waste products in the cells, and certainly there are concerns about the accumulation of protein conglomerates in prion diseases, and the ingestion of polymers, fluoride, and other materials not part of normal human physiology and biochemistry.
So, the thing I have mused about for some time is the removal of these accumulations from cells, and the removal of similar unnecessary material from the body through the lymph system. Perhaps manipulation of the body through exterior means allows the traction, gripping, and dislodging, and moving of things that are trapped - allowing the body to more easily remove them.
I think about it as sort of the inverse, or dual, of 3D printing. We can now manufacture items with captive parts, complex contours, and hollows that are impossible to manufacture by conventional means. Rather than removing material, we add it - around the voids. When necessary, we can use removable support materials.
Physical therapies may be able to manipulate areas of the body that the body can't - either through lack of musculature, lack of articulation or opposable structures, or the absence of things like cilia. Sound might be able to reach areas that physical manipulation can't, or do it more faster and more efficiently. While we can use a brush to remove particles, a sonicator can reach down into hollows and crevices and remove things from places that even the finest bristles can't reach.
There's also the emergent field of sonochemistry, whereby chemical reactions can be promoted through the use of ultrasonic vibrations. So, in the same way that we might use a delayed chemical reaction to get down into and under a particle, so that we can push out from under it, rather then pressing it further down with a brush - perhaps certain sounds can induce chemical reactions, enzymatic activity, protein folding/unfolding, or modulate secondary processes and biochemical cascades which assist the body in doing what it has difficulty accomplishing on its own - through age, disease, toxicity, injury, etc.