Modulating noise will not create a “tone”, but it will give you slowly pulsating noise (a bit like waves on a seashore).
“Noise” does not have “pitch” as such, but a “sweep filter” can give a general sense of rising and falling pitch.
Pulsating noise at 4Hz may not be very relaxing - it will probably sound like a steam train going slowly.
There’s an effect here that produces modulated noise, but the maximum frequency of the pulsation is 1 Hz: Surf-lfo
See the description on that page for how to use it.
Instructions for downloading and installing are here: Missing features - Audacity Support