intermediate shaft noise?

I recently purchased a completely original 79SC w/ 60k on the odometer. After the 60k service (valve adj, carrera tensioner upgrade, leak-down test, ect..) a low chugging (sounds like a piston pump) noise is audible during low rpm idle while the engine is still cold. It goes away as the engine warms up and or the rpms are increased. It was probably there before the servicing but is more noticeable now due to a quieter valve train. My mechanic told me it's the intermediate shaft and that the sound is not unusual and I should not be concerned. Being paranoid when it comes to my first 911 and the sounds it makes, I would appreciate some feedback. Thanks in advance!