Q: Rumbling sound from the exhaust

The AC could have a leaking compressor or condenser, and would need to be checked and tested for the failure. The exhaust rumbling may be the exhaust pipe rusted through. This is common on some of these cars, and would need to be looked at to see if the pipe can be repaired, or if it needs to be replaced. Sometimes, a similar problem happens to the muffler. I recommend that you have a mechanic, like the ones from YourMechanic, inspect the sound coming from your exhaust, in order to make a proper diagnosis.