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!