The RF chokes are about your best bet.
I had this problem years ago when the local AM station, which was about 2 miles north of me, but right next to the same high tension wires that pass near my house. I could hear country music twanging from my toaster, phone, and occasionally, my audio systems, both of them. One was on my PC, with a pair of Yamaha bookshelves and a 12" Sony powered sub. Most of the time, it was barely audible at the volume I normally played it at, but when a trucker running excess power on his CB got close and keyed up, there would erupt REALLY LOUDLY, a mix of the trucker and the AM station. It was always startling when it happened. It sounded a lot like a friend's Macaw talking.
On my main system, I had a full primitive matrix type 5.1 surround set up, with fairly long speaker wires to the rears and it was much worse. Not only was the AM station audible almost all the time, when the truckers got close and keyed up, it would make a loud whine, almost like a siren, and it popped a couple of tweeters. It made my dogs "sing" sometimes. I called up the station and complained about it. They were getting ready to do antenna work, which they claimed, correctly, that it would fix it. In the meantime, for the next 4 months until winter broke, they suggested if I had any extra length on the cables, to coil up the extra length and secure them with zip ties. That did nothing as far as I could tell. I finally bought a large bunch of the "Snap On Chokes" and started putting bunches on them snapped together with as many turns of the cable I was using (10 Gauge car speaker wire) at the speaker and amp ends. It took about 6 on the amp end, and another 4 at the speaker to get it to the point it stayed out of my Yamaha (A Sony, NEC, and Kenwood receivers all did the same thing, just a little differently) R-900 receiver to the point it didn't bother me too much. The only time I noticed it was when a trucker would key up. They could be clearly understood, but they weren't loud anymore.
One problem I could not solve and didn't go away was that the AM signal would be on the outputs of my two identical CD players. One was up on the PC system, and the other on the main one. If I listened to, or recorded to one of my cassette decks, the country station could be heard in the background. No matter what I did, you could still hear it, even with headphones plugged into the player. I found out if I turned off my Audio Pulse delay system, the problem went away. Unless the truckers were close. One day I went past the station and they were working on the antenna. About an hour later, the problems and voices were gone!
