Its possible, I have often heard vacuum leaks; even inside doors, but not usually. One reason for this is that the source lines act as an oriface/restrictor. The air only makes noise where the velocity is high. I would imagine that the source lines/check valves are often a greater restriction than the leak, so your noise will not be at the leak.
If you have a gauge the method I gave above is simple and PRECISE. If its a door lock problem and the car is over ten to twelve years, I would replace all three door vacuum elements and forget the diagnosis. If you fix only a single unit you will soon be back diagnosing the rest one at a time. If you are paying for diagnosis its cheaper to just replace all of them as they are all the same age.
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician