Hohum what can I say I think I may be choking on humble pie! BUT sometimes when the fat's catching fire it's hard to always react appropriately!
Anyway there is definitely a differential and common mode problem, I am sorry to be short on detail but I don't have much in the way of diagnosis tools other than using LTspice to model possibilities and field trials to try solutions. Like I said at the beginning my best tool for measuring results is actually my broadband modem in conjunction with the dslstats software package.
I built the new differential inductor as the bobbin arrived today, I chose to use five strands of 0.6mm wire as the best compromise between current density at various frequencies and the complexity of making it (plus of course what sizes I had available). As I think I mentioned before as far as my broadband is concerned it seemed my lowest easily available frequency of 32Khz is actually better than the higher alternatives.
First three pics show winding, I use the vice in the garage as my 3rd hand holding the other end of the wire. You can see the core gap in the 3rd pic. 4th pic is connected to the inductor tester, result in 6th 4A/cm vertical shows saturation knee at ~13A and an inductance of ~290uH given a 14.5V supply. I should have said somewhere the inductor handles <=7.5A DC or <=6A pk-pk at 32Khz, design flux density is <=200mT.
Installing this inductor on it's own (no common mode) was a disaster, but also re-instating the common mode wound on a blue/green toroid worked wonders, no detectable loss of broadband snr when the solar is in pwm mode at last
The 6th pic shows the installation with the common mode wound with black & green wires to the right immediately at the output terminal block, the new ETD44 is balanced to it's right waiting final physical fixing.
The other inductor on the veroboard with a flux strap is the boost mode output inductor.
Last picture is nice peaceful broadband snr margin, at least as good as it ever gets for me
Guess I should stop blogging now, don't want to annoy anyone........