Virtually all audio gear uses electrolytic caps in the signal path and virtually all electrolytic capacitors need replacing sooner or later. If your audio equipment is 7 to 10 years old it may need caps replaced. If your gear is more than 10 years old it's almost a for sure.
The nasty aspect of electrolytic cap failure is that it happens very gradually at first. For instance, sonic degradation may be occurring gradually from year 7 to year 12, so gradually that if you use the gear regularly your ears will adapt and it's likely that you won't notice the losses (until it’s too late). Some caps fade gradually whereas others fade gradually at first and then die quickly. (Neve V and 8128 owners know about the latter).
Old paper dielectric film caps also degrade and can cause spitting – an occasional or frequent small popping sound.
The symptom of aging caps (they actually dry up and/ or degrade on the inside) is loss of low end and punch and eventually loss of level at all frequencies. The aging will also cause a vague loss of clarity and sometimes a "veil" across the sound.
Audio gear also employs electrolytic caps in the power supply circuits. Aging caps there can result in audible hum in the gear’s outputs.