Locate the screws that hold the toe kick heater in place. Using a flat-head or Phillips screwdriver, tighten the screws to prevent the toe kick heater from shimmying when in use. If the noise persists, move on to the next step.
Examine the toe kick heater for any gaps, which generally occur if the wrong sized toe kick heater was installed.
Fill in the gaps between the toe kick and the cabinet or floor with clear silicone caulk. Run your gloved index finger over the caulk to smooth down the bead, making it less noticeable. Or, using a putty knife, fill the gap with a matching epoxy wood putty.
Allow the caulk to cure for at least 24 hours before using the toe kick heater. Allow the wood putty to dry according to package directions, then sand it flat with fine-grit sandpaper before using it.