The strange problem gets an update.
I visited one of the local music stores today where they have an identical G6118T-135 for sale at the moment. Tried both guitars, in several amps and... no huming from either guitar, in any amp. .
So, my Gretsch anniversary performed fantastic in the store.
My guess now shifts towards if there is any electrical/grounding issues in my flat/in the house..
I have heard fluorescent lighting can cause humming issues.
And dimmer switches too. There are several types of electrical equipment in the home that can cause humming and buzzing in amplified guitars. Take a look at what electrical items are in use in your home and get someone to switch them off one at a time briefly while you use your Anni and amp to try to find the culprit.
Also as a safeguard, checking the grounding of your wall outlets using a simple plug-in tester is time well spent.
I was an electrician years ago ..... absolutelyYes, and LED bulbs, and dimmer switches, and computer hard drives..