Rashi on the Prophets and Writings
Psalms 32
with a lyre of ten melodies Heb. בנבל עשור, of ten kinds of melody.
as a mound Heb. כנד, an expression of height, and so did Onkelos render (Exod. 15:8): נצבו כמו נד, they stood up like a wall, and so did Menachem (p. 121, missing) explain it. נד and נאד do not have the same meaning. He puts the deeps into treasuries under the earth.
He oversees He looks.
He Who forms their hearts together All of their hearts together and knows all the thoughts. Our Sages, however, explain that it refers back to “From His dwelling place, the Creator oversees their hearts together,” and they derived from here that all are examined with a single glance (Rosh Hashana 18a).
You arrive at the cited line; the whole work is yours to read around it. The text is set from the cited public-domain edition.