What are the signs of caps going in an Amp?


I have been blaming streaming since I am new to streaming, like a couple weeks in, new. I was away for a for while as our home was being built and my gear was inactive. I have a Classe CA-151 amp and Classe SSP25 pre that I only use for 2 channel anymore and they are approaching 20 years old. So I bought a Node 2i and have been enjoying my Qobuz trial. It started intermittently the last few nights where I start hearing static, muffled sound, almost like a radio station going softly in and out of tune. I have been blaming it on streaming and wifi or ethernet connection. Someone pointed out it may be a cap starting to go bad. I checked all the other connections and everything is tight and good. What are the signs of a cap going bad? Is it constant or intermittent? Next time it happens I am going to switch over to CD to rule out streaming. When it happened last night I switched to Tidal to rule out Qobuz, and then switched to my MacBook to rule out the Node and it was still there. I did not have the CD player connected at the time otherwise I would have switched, but that is my next step. 
Thanks!
128x128jmphotography
Speakers are about the same age as the classe? I had a speaker that would distort only on certain songs found out it was a loose connection in the speaker. I would try the CD player if  you hear the same distortion you can use the process of elimination. See if it's both speakers you hear distortion from, switch one cable at a time around try to narrow down what's exactly causing it. Could be anything. 
Honestly it sounds to me like you may be having an RFI issue is anything near your streamer like say a modem or router? Also do you have any lights in the room on dimmer switches? From how you've described your system and the noise it sounds external not your gear.
@jond No dimmers in the room. But we do have an outlet that is connected to a smart home wireless setup to control lights in the room as well as a light switch in the room where the router is located. The router and modem are in a closet in the room one floor above the system. The system is on a 20A dedicated line.