load noise after starting
A few things on you note do not make sense to me.
1) Your low pressure alarm should shut off well before 125 lbs since normal operating pressures are between about 90 and 130 lbs.
2) You mentioned a pressure of 10 lbs. Please note that the single pressure guage on the left of the wheel is a turbo boost. The two airbrake guages are located on the cluster to teh right of the wheel.
3) The compressor for your airbrakes is designed to operate at all times when the vehicle is running. Once the maximum pressure is reached, you should hear air being released by the pressure relief valve (like when you are on a bus).
4) A load ... gun like noise comming from your coach is not normal. If it continues, I would highly suggest taking it into a Freightliner dealer for an inspection.
5) Once of the posters suggested getting you airbrake ticket or Q certification. Speaking from personal experience ... this was some of the best money I have ever spent. Air brakes are very different from the type of brakes that you have in you car .... it is possible to get yourself in a whole bunch of trouble in a really short time . Example ... if you are someone who rided the brakes on a hill, it is possible to very quickly use up all of the reserve air in the two holding tanks.... at which point you loose control of your brakes and you are in danger of your brakes locking up. Example two ... if you have a leak in the system and do not stop teh vehicle before all air is depleated ... your brakes will lock up with over 3000 lbs of force and will require professional service to release them. (Image this happening in the middle of a rail crossing with a train coming).
I have gone through the unpleasent experience of having one guage falling to zero as I was driving on a mountain road. This was one of the most stressful times of my life.
Please do yourself and those around you a favor and get your airbrake ticket. It takes 2 days and cost about $100
Once you learn how to use them ... you with love the combination of air brakes and engine retarder