f/u to sound sensitivity

My DS is almost 23 months, has an isolated speech delay and has been receiving speech therapy for about 4 months.  He's doing really well (from zero words to over 100 plus a few 2 and 3 word phrases) and we are really pleased.

We have a few lingering issues though.  He is very sensitive to sound. We live in a two story town house and he will stop what he is doing and hold his hand to his hear, cupping it, whenever he hears a blower outside, or a garbage truck or an airplane overhead (we live under the flight path, oh joy).   It made him a ridiculously light sleeper for a long time (even with a sound machine in his room to drown out outside sounds). 

His speech therapist suggested having his hearing checked to see if he was hypersensistive to sound.  Her concern was that if it interfere's with his sessions with her at home, it is likely to interfere with his attention ability at school. So we did.  We told the audiologist why we were there, she scoffed like we were fools, and performed the standard audiogram -- we sat in a booth and he turned his head towards her voice.  Fine.  She checked for fluid (found none) and the shape of his inner ear (also fine).  She said his hearing was normal and sent us on our way. 

Our therapist thinks it wasn't the right test or done correctly and I don't know what to do.  Our health insurance paid for the hearing test and it was done at their facility, ordered by the developmental pediatrician who evaluated our son and knew what we were concerned about.  The therapist is from EI.

Is there some other test to look for hypersensitivity to sound besides an audiogram?  Any tips?