Hissing when I start the car

#1

I am driving a 2002 Subaru Forrester and I just had everything done under the hood. Now when I start the car there is a hissing sound that doesn’t last long-but is troubling-any ideas

#2

vacuum leak?

#3

I agree. Most likely, the mechanic who did “everything under the hood” also wound up disconnecting a vacuum hose. It looks like “everything” is a longer list than was desired.