I'm currently trying to figure out why I have to recharge my AC every spring I'm looking for leaks. Question is what are the sections of tubing that have the tin foil like tape on them? The one behind the battery I can hear flowing or leaking in it after turning the truck off for a minute or so.

The leak is probably at the evaporator under the dash or the O-rings at joints.  That tubing behind the battery is the high pressure line coming from the condenser going to the evaporator and the expansion valve is in that line.  The noise you're hearing is the pressures equalizing at the expansion valve. 

So that's a normal noise? I changed the evaporator last fall when I did the heater core and today I changed the valve things in the high  and low ports. 

Another spot that seem to be impossible to find the leak is the compressor front seal. It won't leave dye and impossible to snif while the truck is run with a fan blowing.