Already time for a cooling system rebuild.

I have to agree with pressure check the cooling system first. A small hole in a heater hose, a freeze plug, etc.. could let water get away slowly. Its gonna run hot eventually. Groaning noise would be radiator cap venting pressure. If the cooling system wont hold pressure but no visible leak, pour some water in it and start it up. If you get steam out the exhaust.... head gasket failure. Good luck