We have an ultrasonic stethoscop for this from SDT. Also usefull for controlling bearings but we use it mostly to control the sealings of refrigerator and freezer doors.

I fI haven't the SDT with me (most of the time ), I use same method, pulling vacuum with compressor itself.
If it rises slowly and stops at 'ambient pressure' -->Low pressure reeds, if vacuuum breaks fast, mostly associated with very hot head temperatures --> high pressure reeds.

If compressor is not older then 5 years, or we have one bigger then 10 HP (the more expensive sorts) , we then do the following: open up the compressor head and turn the reeds 180° (if they're not broken of course)
Sometimes you see that the reeds are worn out a liitle bit with a little ring pressed in it (the circle of the valve plate itself).
Then do the test again and if problem remains, replace mostly the whole compressor if below 5HP and not older then let's say 7 years.
A new valve plate with gaskets is too expensive to take any risk.