Think my heater core is going bad?

If only 1 heater hose is hot and the other one is cool, you have a plugged core.
Take both hoses off at the engine end.
Reverse flush it thru the cold hose a couple of times and see what comes out.

As for the noise...pull the fan motor out and check for debris in front of the core. 40 years of crap coming thru the cowl has a tendency to collect there.