2002 Toyota Camry vacuum system

Hi, my car makes a "whoop" sound intermittently when I drive. It seems to be at any time and at various volume and pitch. I notice it more when I go from deceleration (foot off the pedal) to aceleration, at slow to average speed. Most people I've asked about it says it's the vacuum system. Since it doesn't seem to affect the performance of my car, it this something that I need to get repaired and how much should it cost?

Thanks for any informaiton you can provide.