It's just means you have a shitty audio tract with not enough shielding. Move to SPDIF/TOSLINK.

I have an external audio card, if I put it on a laptop I can hear the modem-like sounds. I wonder why it is so sensitive, should not DAC produce strong signal that cannot be easily affected by radio waves?

Also my headphones are extremely sensitive. I can touch the ring and sleeve of a jack with a finger, and touch a metal bed frame with a tip and I hear quiet clicks as I move the tip along the metal. Sometimes I do not even need to touch the jack with a finger. It doesn't work with small objects like a knife though.

Bad grounding everywhere. This is insanely basic stuff.

the radio waves could be interfeering with the signal before it gets amplified