This is my setup
Raspberry PI4 with 8 GB RAM; boot via Sata SSD (in enclosure) connected via USB3
1 USB2 extension cable + Hub which goes to 1 RTLSDR dongle (for ADS-B) and 1 Airspy Mini (for ATC communication). The ADS-B dongle is obviously running all the time with piaware while the Airspy Mini is only used when I tune in to listen to something so...not often.
1 USB2 cable which goes to a third RLTSDR v3 used to capture satellite on a certain schedule.
The two RTLSDRs can run at the same time without issues. However, if I try to also run the Airspy Mini (that is, tune into a frequency) while the others are running (could happen as I don't realize if there is a satellite pass at the same time) then the raspi makes a weird high pitch noise and It basically freezes. I get I/O errors and I cannot do anything as no command is found: I guess the SSD just disconnects itself from the USB. Only way to fix it is to restart.
Is this related to the USB bandwidth? I thought the Raspi4 was capable of handling these simultaneous connections.
The problem was power-related. Once I introduced a powered USB Hub I never encountered this issue again.