How do I attenuate 30kHz noise?
Put linear regulator before uC - they will react fast enough to cut low-freq noise. Especially good if you have some margin between power supply voltage &amp; uC voltage.
Just add large(some 10-1000 uF) caps before uC: some electrolytic and some 1uF and 0.01uF ceramic ones all in parallel to prevent resonance. Ceramic ones should be as close as possible to power pins of uC. If it were more powerful uC, I would consider adding ferrite bead, but it might be not needed in this case.