what is the mechanical hound's reaction to montag? what is he worried about ( he will say this in his conversation with captain beatty)?

From the text:

"The Hound growled."

Montag is worried that someone has been messing with the hound to get him into trouble.

"All of those chemical balances and percentages on all of us here in the house are recorded in the master file downstairs. It would be easy for someone to set up a partial combination on the Hound's 'memory,' a touch of amino acids, perhaps. That would account for what the animal did just now. Reacted toward me."