My girlfriend has a 2001 Jimmy. Recently, at intermittent intervals, there is a high pitched (appears to be electrical) whine that fluctuates with pitch according to RPMs. There does not seem to be any rhyme or reason as to when this occurs, but when it stops, all the warning lights on the dash cycle through and the noise goes away. Does anyone have any ideas what this could be? The noise cannot be heard outside the car. Thanks in advance.