T30 model 2340 is leaking air from around the pressure switch when compressor shuts off. This will last for a few minutes and then when compressor starts and stops it will do it all over again
Air Tools & Compressors - Ingersoll - Rand 2340/2475 Electric Air Compressor Start Up Kit 32305880
Answers & Comments
You have a broken valve. follow the small 1/4 line that comes from the pressure switch, and if it goes to the discharge line from the pump to where it enters the tank, there is a large hex fitting that it is hooked into. drain all the pressure off the tank, and remove the fitting from the tank, this should be a check valve and is stuck open.
If the small line goes to an innerstage cooler between the large and small cylinders, then you have a broken valves in the cylinder head that need to be rebuilt.