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I assume when you say “knock” you mean the hand throttle knob assembly, correct? Was there any checks done before replacing the hand throttle? Example hand throttle voltages or percentages reported in the instrument cluster diagnostic screens, or fault log in the instrument cluster menu.
From the description, and assuming there are no fault codes or warning messages, then it sounds like the hand throttle is being deactivated due to certain normal conditions present/detected. These conditions would not generate faults that I am aware of.
Here are some initial things to check
1) Pressing a brake pedal will cause the hand throttle to be deactivated. Make sure the brake pedal switches are not out of adjustment or damaged causing a brake switch to trigger by vibration during hammering.
2) Rotating the seat will cause the hand throttle to be deactivated. Are you “fully” rotating and locking the seat when operating in backhoe mode? If you are operating the backhoe while the seat is partially rotated and not locked, the hand throttle could be deactivated as the seat rotation switch could be actuating. Also make sure the seat switch and wiring is not damaged.
Let us know what you find.