Yes, I understand the principle. I have look that with oscilloscope.
I can test with a 2nd Mosfet
But in fact the T/R signal coming from the arduino is more "short" as the "time of descent" of the TX power supply during the rollover.
So in a little time your have the 2 supplies.
The simplest test to prove that this comes from is simply disconnecting the TX from the relay.
we’ll see if that unpleasant noise goes away then.
Other solution increase the T/R time by soft. This may be possible.
Otherwise, you did not tell me if you also had this noise when turning the encoder. It is also a 2nd problem a bit annoying.