As discussed in the 4/26/2008 morning show here in Seattle
A woman with a 1999 Subaru with a ‘high pitched whistling’ sound and I shared that same experience. It turned out that my stereo was not grounded correctly and the speakers were providing feedback from the alternators electrical oscillation. When I revved the engine it would increase the oscillation and the pitch would get higher; also, the volume of the radio coming through the speakers gave the feeling that the sounds were getting louder. I believe that when the consistent, harmonic sounds of the engine were overtaken by the loud, inconsistent sounds of the radio, I was more attuned to the high pitched electrical feedback coming through the speakers.
I was thinking that the older gentleman mechanic may have been listening for the sound from te engine compartment rather than the passenger compartment. The discussion in regards to higher pitched sound loss in aging people is accurate and would also apply to the speakers feeback. (http://hypertextbook.com/facts/2003/ChrisDAmbrose.shtml)
I grounded the audio system properly and was immediately relieved of one of the most annoying experiences I ever participated in.