Radio interference - B3 Burns

Hello everybody, long time reader, first time poster at Theremin World. Nice to meet you all!

I'd like to ask some advice for a prickly problem I'm having. I have a B3 Burns Deluxe which I've been playing for around 1.5 years (slowly working my way through Carolina Eyck's method book). Around 6 months ago I began to get some really intrusive interference from a local AM talk radio station - not very loud, but loud enough to reduce the sound to scratch and gravel and throw off clear intonation. I contacted Dan Burns and sent it back to be re-tuned, and that worked well at first, but just recently the interference has returned again.

It's intermittent, some days the instrument sounds clear and others it's barely playable. For reference, I'm using a battery powered Bose speaker and a small 6V battery pack to power the actual theremin (I run it all cordless because if I use the power supply provided it howls like a broken hair dryer. It only has two prongs so I suspect it's an earthing issue. Same goes if I plug in the speaker, though noticeably less so).

I've tried retracting the antenna to various segments and also clearing away all other electrical devices and cords from the area. I've also tried moving to different rooms and even outside but it still persists. I have a lot to learn about the technical aspects, so I'm sure there's something I'm missing. Is there anything else I can try, aside from living in a giant Farady cage?
Thank you for taking the time to read, I appreciate it.

You need a better earth ground. 

Run a wire out the window connected to your own copper rod, several feet long, pounded into a damp flowerbed.

Here is one of the finest "authentic theremin" sound and performance. 

Christophe
Old Temecula

You need a better earth ground. Run a wire out the window connected to your own copper rod, several feet long, pounded into a damp flowerbed.
Here is one of the finest "authentic theremin" sound and performance. ChristopheOld Temecula

That's an amazing performance, it sounds wonderful. 
Thanks for your advice. Regarding earthing, I'm using a mono cable with a metal right-angle jack, would it be prudent to attach the earth to that, or should I attach it to part of the instrument itself?

"Around 6 months ago I began to get some really intrusive interference from a local AM talk radio station..."  - Norem

The Burns uses RC oscillators which don't have much in the way of selectivity so they can probably pick up anything in the vicinity.  Get a Theremin that uses coils in the oscillators.

The Burns uses RC oscillators which don't have much in the way of selectivity so they can probably pick up anything in the vicinity.  Get a Theremin that uses coils in the oscillators.

Thanks for the info, I'll be upgrading in the future once I'm a bit better at playing the instrument.