What is your gain now? Higher gain pushes the noise higher, a good preamp has low noise and lets you lower the receiver gain.
I usually tweak it manually, in short bursts, when the traffic is high in the area (not at night, then it can be higher, but I don’t care that much for the few planes).
Change gain, restart the service, look at the local webpage for results (number of planes and msg/s). After they “stabilize” (15 sec or so) I do it again in small increments around that value.
Supported gain values (29) are: 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6
I have the add-on piaware, so for me, those are the commands.
sudo nano /etc/default/dump1090-fa
sudo systemctl restart dump1090-fa
If you are unsure of the active setting, you can check it with:
sudo systemctl status dump1090-fa -l
I hope you know that, in the command window, pushing the “up” arrow lets you scroll and re-use previous commands in that session, so you don’t have to compy/paste or type in those every time.