I assume you have a choke on yours?
If you don't then, as far as I'm aware, you should.
You don't need to buy on. Just give Ron a bell and ask him how many turns, etc. on his and wind one.
Just in case there is RF coming down the feeder.
As you have to beam at the house, this is not likely to be the problem.
It's probable that the loudspeakers on the PC, powered ones I assume, have cables that are resonant at 4M and are horizontal.
FM, obviously, will not be demodulated as it is a constant carrier level.
AM, and SSB, since they are amplitude modulated will be detected by the input circuit of the powered LS and produce audio.
No amount of messing at your end will fix it if that is the case.
The fault is on the powered speakers which are doing something they should not.
I've a similar problem here with 400W at 6M, when I point at the shack.
Ferrites cured it.
Any work you do at his end, ferrites etc, is fixing the problem, not masking it.
They are powered speakers, not a radio receiver.
It's possible that just re-arranging the wires at his end might make a difference.
Going for a Yagi with a narrower beamwidth might make it that the effect is over less of an angle as might raising it but I'd go for the ferrites and moving/changing the length of the cable.
Just explain to him that it is a common design problem and they should not act like a radio receiver.
Do you get anything in speakers on your PC?