What would cause multiple spontaneous pin hole leaks in copper plumbing away from joints or wall nails?

10 pin hole leaks over an 18 month period in different pipes - near each other, but not caused by any obvious physical contact with anything.What would cause multiple spontaneous pin hole leaks in copper plumbing away from joints or wall nails?
As there are several grades of copper pipe who ever did the plumbing probably used the thinest and cheapest. I had the same problem and ended up replacing everything after I got several leaks behind walls causing lots of damage and headaches. Get a good brand of copper pipe ( I forget the grades but they are letters such as ';M';) so check with your hardware guy and get the good stuff and not the stuff from China. Also be sure your electrical system is grounded to a ground stake and not to the plumbing as some shady builders do as this also can cause you problems from electrolsis. Another option is using plastic pipe it is everywhere now and is very good stuff.What would cause multiple spontaneous pin hole leaks in copper plumbing away from joints or wall nails?
I can Only think of 2 things. defective pipe alloy(replace that whole piece of pipe) or, It is being used as an electrical ground and electrolisis is weakening the pipe. google( copper water pipe electrolisis) this could very well be it.