Then it is not the fault of your radio, you can recreate the conditions of quiet and noise in their same areas by revisiting them consistently - and if the noise appears then fades as you leave, well the radio isn't the problem. Nor is it the operator.
The noise exists because it's external to the radio - and you can only do so much to reduce the noise - RF gain turned down, Noise Blanker and ANL filtering but then that is not stopping the noises at their sources.
It's frustrating - yes, I have this similar problem too. Just have to relocate to another location.
Now if you try another radio - you may have similar results. That is the only other options we have - changing antennas may help a little for the same radio , but this sounds like a noise problem in the area you live. Not much you can do. Putting in a mod to see if it can help is not always the best option - I just don't want you to become frustrated at trying to find a working solution - it seems you've done your homework.
I'd hate to think that the radio is TOO sensitive to the noises but then that simply means you just turn the RF gain down on the radio - let it do the filter work for you.
Also - use the Clarifier in RX - if the Clarifier has been opened up even better, for then you can "center in" on the station you're talking to. This can help with that noise - you simply line up to each other and talk thru it.
Just some ideas...