For people with hearing loss, the sound signals from the inner ear to the brain will be weaker than normal, and it's possible that the brain amplifies these signals too much to compensate, resulting in hypersensitivity. However, this doesn't explain the cause in those with hyperacusis and no hearing loss.
Bicycle Valve Stem Types. There are three types of bicycle valve stems in use: Schrader, Presta and Woods/Dunlop. The Woods or Dunlop valve stem style is much more rare than the other two. Any wheel rim that fits a Schrader valve can also fit a Woods or Presta valve.
These bikes are equipped with Schraeder valve inner tubes. The rims require a longer stem than a standard schraeder valve has, and so the bikes come with a long stem schraeder tube. This has made long stem schraeder valves somewhat available in bike shops, at least around here; I don't think Wal mart sells them.