Battery-Powered Audio System Buzzing?

To follow on the already correct advice from @cleeds , it's a lot cheaper to provide a square wave output UPS than a sine wave.  Unless it specifically says "sine wave output" it probably is not.  

The square waves produce a lot of higher frequency harmonics (relative to 60 Hz) that make it through the power supplies.  Also make sure you don't have your system grounded through some other means, like using 1 device which is not battery powered but some that are.  It could do weird things in terms of the ground voltage.  This includes coaxial and USB connections. 

Quality batteries with the correct match up can deliver clean power. In case your case, your system is putting too much demand on your small battery. No chance of delivering consistent clean power at any point. I have hooked up my Yeti Goal Zero 1500 with my Accuuphase and streamer with good results. Being a class a/b amp its putting very little demand on inverter. Drawing about 100 watts. With your system being demanding for power, even the Yeti 1500 will not get you there. Also, not all batteries inverters are equal. In my opinion, a battery to meet your clean power needs is cost prohibit. Cost benefit does not pencil out. 

Thanks to everyone for the input. I confirmed that my Anker battery creates a pure sine wave. It also has a maximum output of 1800 W, and my system on average draws about 175 W. @erik_squires thanks for the suggestion, I had not put everything in the system on the battery. Once I did the buzz basically went away. Thanks again!

@sid-hoff-frenchman , do you hear an improvement when using the battery versus plugging into the wall?

If you are going to use a battery in hopes of hearing the effect of quieter power, it makes sense to try to use the batteries power directly without interposing an inverter. What I mean is that a battery supplies direct current. The interior circuits of all hi-fi equipment Use direct current. Why bother changing to alternate current only to have to convert it back to direct current? The easiest way to do this is to use hi-fi components that employ an external DC power source (the infamous wall wart) generally, these will be less expensive but nonetheless high-quality sources, Dacs , and amps such as a raspberry pi based streamers, topping dacs, and Fosi amplifier just as one set of examples. You will need to find separate lithium ion batteries for each component that match. It’s voltage and amperage requirements, but this is not too hard to do and considerably less expensive than the large battery solutions already discussed. I have done this and have been very pleased with the results.