For the power supply cap gone bad, you will hear a 120 hz hum;
Crackling and popping noises from the speaker can be bad electrolytic caps in the tone circuit (balance, bass, midrange, treble);
A bad electrolytic cap on the feedback circuit can produce lower volume or higher distortion at moderate to loud volume setting in one channel.
As an aside, I took out of storage my 40-year old Marantz 235 receiver that hasn't been powered up in over ten years. The 10,000 uF power supply caps measured 9,600 uF with 0,02 ohm ESR. Practically like new. But it did crackle and pop a bit so I left it powered on over a variac at 20 volts for 48 hours to reform the caps and it sounded like the day I got it. Those vintage equipment give meaning to they don't build them like that anymore.