What are "Havos"?
Rashi: They are breakages [Radak - and an evil matter].
Why does it say "Lo Yamish me'Rechovah"?
Radak: They always engage in Toch u'Mirmah against me. They gather in the Rechov (town square) to talk about this.
What are "Toch u'Mirmah"?
Rashi: They are an expression of a plague.
Radak: Toch is like Mirmah 1 . It uses this expression, for he shows with his mouth what is not in his heart. His mouth speaks one matter, and in his heart is another matter 2 .
Metzudas Tziyon: It is Mirmah hidden Toch (inside) the heart.
Malbim (Yirmeyah 9:5, Bi'ur ha'Milos): It says "Alah Fihu Malei u'Mirmos va'Soch" (10:7). Toch are words that have two Perushim; amidst this, he tricks the listener.
Radak: Also their mouth plotted against David! Rather, when David was among them, amidst Mirmah they showed love. If they truly loved him, they would not conspire with Avshalom!