LM2576-ADJ Unstable Output
With 100uH inductor, 52kHz switching freq., 12V to 5.35V conversion and 1.33A output current (4 ohm load) your inductor's current will go 0.6A peak-to-peak. Be sure your capacitors are Low ESR and able to handle at least 0.3A RMS current. 

I see some major issues with your layout design. I don't think they will result in 1V p-p, but I think you should consider them to design a good DC-DC converter.

1) This schematic has only 1 sensitive node - the feedback divider and you have placed it right under the inductor when magnetic field is strongest. Move it somewhere else.

2) The ground connection for R1 should be taken alone from the closest low impedance capacitor - the ceramic one will be better. You take it from diode's anode where pulsed current flows.

3) The output voltage connection for R3 - same thing - noise from inductor. 

4) The ground connection of the switching IC - 2576 - too far away from output's filter capacitors.

When designing SMPS first you must examine well where the largest pulsed current flows. You should keep these traces as shortest as possible. The ground pin of the control IC must be as close as possible to input and output capacitors' grounds. The feedback and any low current signal must be taken from a low impedance source with highest possible filtration. Making "star points" near capacitors and powering different nodes with different traces is better. 

Think of the copper on the board as a resistor, not just the "ideal short"!