Loss of vacuum is a warning sign for the bearings letting go in your vacuum pump, This being my second experience with this same failure I feel safe to say this is your forewarning before tragedy . So if your engine seems to not shut off right away don’t blame a line leak , It’s most likely your pump has a greatly reduced function , this being it’s not getting the full throw of motion with missing bearings in its cage .I noticed the familiar ticking from the front of the motor and knew to open it up , so yes , their is an audible sound with every revolution of the motor . Unfortunately the pumps are very rare to find ,a rebuilt one is $500 plus these days! Ouch