Sorry if something like this has been posted before.

I recently got a cheap epiphone sg from a friend of mine.
Ive been playing guitar for about 5 years now (my main setup is a Gibson Les Paul Classic through a mesa dual rect or roland jc-120 with a boss gt-8) but i wanted a really cheap guitar to just mess around with
but ive never encountered this problem.
the guitar is just fine when its not being touched
but whenever i touch any metal parts (bridge, strings, input jack, etc.) it buzzes

please reply with answers to my problem

and again i apologize if a similar problem has been stated before. (im new to these forums and am not sure of whats on here)
sounds like you have a grounding problem. check the electronics and see if any of the wires are touching that shouldent. your ground might not have enough cantact. the round wires should be on the right side tail piece stud. im not sure if its the tail piece or the intonation peice if it has one.

hope i was of some help