Allnic H-3000 hum when mute button engaged.

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~

@lewm- you may already know this, but Bill Thalmann is authorized to work on the Allnic gear. And I agree, he is first rate. He restored a bunch of vintage gear for me that give me great joy in my second system. Nice man to boot. 

@dangcaonguyen - I agree that you should speak to seller first before you open up the unit or commit to spending money. May still be worth talking to Albert about your options. Perhaps it is a simple fix, but presumably that’s going to be out of the seller’s pocket. (and you’ll need to find a decent shop near you-- I hate shipping gear if it can be avoided; I actually dropped off my stuff at Thalmann’s en route from NY to Texas).
Assuming the unit is already out of factory warranty period, the main concern- once you reach agreement on approach with your seller, is to avoid a situation where the manufacturer says "oh, you let someone unauthorized work on it, so in the future, you may have problems getting service." Frankly, I don’t think Albert would jam you- and the support I got through David Beetles (and subsequently Albert) has been first rate- they have the relationship with Mr. Park, and it makes it way easier for them (now Albert) to guide you. Hopefully, you get it sorted fast, cheaply and easily. Let us know what happens.
I would think there would be some good techs in your area.

Good catch. I didn’t even think of that. Hope that solves the problem.
Then you can get down to the serious business of rolling rectifiers. :)

Calvin- quite a few threads on the subject. A lot of the rectifiers are cheap enough that you can try several for yourself and see what works best in your system. I am presently using a GEC U-52, have used a fat base first series Mullard (the earlier metal base is preferred) and there is a military RCA from WWII with a particular getter arrangement that is supposed to be good. (Perhaps that's what's in there). You might look at Dub-Step Girl's Massive Rectifier Shoot-Out (or something like that)-- she does describe the general character of many rectifiers, but I think the results will still depend on the circuit and what you are chasing in the system.
I'm glad the problem was simple to address. Enjoy your new phono stage!