Was the Buddha known to chant during his meditation?
During his developmental years (before he became Enlightened) he might have.
This is because mantras are a way for you to match vibration with a particular deity and thus receive their assistance.

The Buddha gave many such great mantras including the Zhunti mantra but a Buddha has no reason to use them because the Buddhas are all connected simultaneously through their uncovered dharmakaya/Tathagatagarba/Buddha-nature.