How to prevent switching direct and/or inductive noise on a PCB?
For lowest noise, you need GND of C4 next to GND of D7, TO MINIMIZE that loop_size/radiation/voltage drop. Why? The slewing of the diode voltage (input to energy storage inductor) will be the fastest node in your system. Keep that PCB trace very small in area and very short in length (which also reduces the radiative loop area); and have a trash collector (piece of copper, tied to Gnd) under that very fast 24 volt switching-reg node.

For less "singing" at the 60 Hz rates (or 120 Hz rate) from very fast current_turn_on thru the bridge rectifier, insert 1 uH inductors or 1ohm resistors in series with 1 leg of the bridge.

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Does everything look fine? What are your noise goals? (for lowest noise, use a 2nd layer as GND plane.)

Is this to evolve into a commercial project, with formal must_pass_FCC measures?
Is so, why not START by using a GND plane?

Have you considered how to remove heat? A 1_layer PCB will be horrid at heat removal because the epoxy_fiberglass will define the heat flows; FR-4 has 200X the thermal resistance of copper for equal thickness; the ratio of thicknesses is about 0.060 / 1.4 === 40X, so the heat flows will be very limited; expect local HOT SPOTS.

To understand this, get a quadrille paper pad, and start drawing heat sources and heat exits, realizing each square on the pad is an increase in temperature.

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The 60Hz (120 Hz) singing is the narrow/fast turnon time of the DIODES in the bridge (4 diode) rectifier. Assuming most of the turnon current occurs in 0.026 volts (when the current thru a diode increases by e^1 = 2.718^1  = 2.718X), your turn_on time will be the SlewRate of your unrectified power transformer output, divided into 0.026 volts.

Assuming SlewRate of transformer is 40 volts peak * 377 radians/second (from taking the derivative of 60Hz sin, with 6.28 * 60 == 377) or SlewRate is found to be about 16,000 volts/second. the turnon time is 0.026 / 16,000 == 1.5 microSeconds.

Thus your 60Hz rectifier diodes are a 1.5 microsecond fast-edge high-power interference generator.