[RFI] Power line noise question for the experts

[N1BUG]

I have successfully located multiple sources of power line noise and 
the power company has kindly fixed them. At this point 90% of the 
noise has been eliminated but what remains is still quite 
bothersome. I am having considerable difficulty getting positive 
identification of the remaining source pole(s).

The noise is present from at least 1 to 60 MHz on the home station 
receiver (no equipment for higher frequencies). Looking at it with a 
scope there appear to be two intermittent sources of noise, one each 
on two different phases. The pulse count on each is highly variable, 
usually just one or two pulses per positive and negative peak on 
calm day, rapidly varying from none to many on a windy day.

At 135 MHz (3 element yagi) I cannot resolve the source pole. Noise 
is strong and nearly constant along a stretch of 7 poles but drops 
quickly beyond either end of that area never to be heard again (I 
have checked the line 2 miles in both directions from there).

At 445 MHz (7 element yagi) I cannot detect it at all.

Given that the noise is quite strong at 135 MHz but not detectable 
at 445 MHz, is it likely some frequency in between might help in 
resolving the source pole(s)?

The poles have a 13 kV distribution line with a 46 kV transmission 
line overbuild. I have reasons to believe all remaining noise is 
from the 46 kV.

On windy days I have been able to hear ultrasonics from two 46 kV 
insulators on one pole about in the middle of the 7 pole stretch. 
The highly variable ultrasonics partially correlated with variable 
noise from the station receiver (listening to both at the same 
time). The correlation left something to be desired and I was having 
great difficulty holding the dish steady in the wind. On calm days I 
cannot hear ultrasonics from the suspect insulators. I would like 
more/stronger evidence this is the source before asking the power 
company to look at this pole for the third time.

Any tips or suggestions?

Paul N1BUG