I've worked with a large local PV installer to solve RFI problems, and I
can vouch for the fact that it can be difficult to de-noise PV
interters. the MPPT circuit is not analog and can turn the DC input
lines into hash antennas, and as you stated, the inverter itself can put
RFI on the 120/240 interconnect.
When I was in the market for PV equipment, I took a small battery
operated emergency radio and visited several sites as well as showrooms
of local vendors where they had demo systems. The quietest PV install I
found used the SMA 3000US inverter. I just looked on-line, and the
closest I could find to this model is now called the 3000TL
(transformerless) so I cannot vouch for it's RFI characteristics.
I installed it using a combination of EMT and BX wiring to shield the
input and output wiring, with twisted conductors in the conduit, adb BX
having inherently twisted conductors. I see zero increase in my noise
level due to the PV system from my 160M OCF which goes right over the
house, so I can definitely recommend that model SMA. They are not the
cheapest inverters, but as a student of switching supply design, I know
the least RFI-generating topologies are not the cheapest, and good
transverse and common-mode filtering is not cheap to implement at the
power levels a PV system can operate.