My iPhone 13 makes hissing sound after connecting calls

This may help --> Hear No Sound or Distorted Sound Issue Po… - Apple Community

Like from the iPhone or on the software? I’ll list some options.

1. Restart your iPhone.
2. Replace it (if it’s the hardware) this could be very dangerous.

I have the same phone, and it doesn’t do that. Are you on an old iOS? If not, replace it immediately.