Allnic H-3000 hum when mute button engaged.

No
I've never been near an h3000
you need a pro

Return it and get your money back! 

Sorry for the brevity of my first response to your question about how to open up the case of the H3000. I was typing on my iPhone. I have no idea of your level of knowledge and experience when it comes to working on audio equipment, so that response was based on an assumption that you are not, in fact, experienced. You’ve got a very expensive, very fine piece of gear there. I would not advise you to service it yourself. If, however, you know what you’re doing, you probably by now have figured out how to open the case. Let’s assume that you do find a problem that is as obvious as a loose, unconnected wire. Would you know how to solder it back into place and what it should connect to? If the answers to those two questions are not yes and yes, it would be worthwhile to find a competent tech.

By the way, in my experience, problems like this rarely are as obvious as as a "loose wire". A bad ground could be caused by a cold solder joint that may look fine by inspection.

I don’t agree with Yogiboy, by the way.

@yogiboy The unit operates perfectly, and the music sounds awesome. I really don’t want to return it. And I think the mute button is sn easy fix. I am contacting the seller to see what he will say.
@lewm I know how to soldier, it just I am afraid I will damage the unit by opening it up the wrong way. I have made my own intetconnects, so I think this job is not hard for me if I could open it up. 

if you reach out to Albert Porter, he may be able to help guide you, with all the appropriate disclaimers. Never heard of this problem, but dig mine. He might also be able to tell you the age- there was a running change on the unit roughly 5-6 years ago involving transformers and a few things in the power supply. 
Love mine. 
Roll the rectifier tube- lot's of threads on that subject. Big differences, and some of the good ones aren't crazy money. 
enjoy~