MR might have something there.  When my son was being overdosed he would startle over everything.  Then he would yell at us as if we did it on purpose.  I would walk into his room and say his name at a normal level and he would jump and cry saying that I scared him.  He was 6 years old.

He is now 10 and loves his music loud.  The louder the better.  He plays the guitar, trumpet and piano.   He and two of his friends come over and they "jam".  They have named their band and get together at each other’s houses on a regular basis.

Check your child’s levels.  This time they may be over suppressed.  My brother-in-law admits to using steroids when he was lifting weights.  He told us that sometimes the sound levels would send him over the edge and he would have to get out of the room.  His temper was short and reaction was quick.

I hope this helps.