My '01 X5 4.4i sounds like it has asthma

[sandy eggo]

I've done some searching through the threads and it seems like a few others have had this problem.

General description: Upon starting, I get a whistling/whining sound from under the hood - imagine a car with asthma - it's got that "old car sound". In the beginning, this annoyance would occur only sporadically and used to go away after the engine warmed up. Gradually though over the past 3 months the sound has become more prevalent - staying audible for entire drives (30 mins+).

A shop I get work done at believes it is the secondary air intake that needs replacing and with (a lot of) labor, parts, etc may be around $900 to do the job.

From the threads I've found on this website, it seems like it could be a crack in the Intake Control Valve hose?

Any other thoughts on what this could be, how serious the problem is and how $$ it should cost to fix?

Thanks!