CE-680 Captain reported a pitch trim malfunction during the climb; after flap retraction. The flight returned to the departure airport and landed.

Narrative

Pitch trim jam after takeoff. A normal takeoff was conducted out of ZZZ. At gear-up; pitch trim appeared to actuate correctly. At flap retraction; pitch trim appeared to stick/jam at -2.8 degrees. This was initially misdiagnosed by myself as a pitch trim runaway due to a stuck trim setting and a rapidly accelerating aircraft. I performed the memory items for a pitch trim runaway. An immediate return was started. Priority handling was requested. The aircraft was banked left to begin a left traffic pattern. Auto throttles were disconnected and power was brought back to slow the aircraft. Pitch forces were relieved by the bank and reduced speed enough to gain situational awareness. Secondary trim was then utilized to pitch the aircraft downward. During the chaos; a loud thunk or thud was heard. I cannot remember if it was before or after the use of secondary trim. The first officer heard this sound again when in the downwind. Passengers also remarked hearing a loud thud noise in flight. The landing albeit chaotic; was uneventful. There were no injuries to passengers or persons. We were met by priority handling vehicles. The aircraft was stopped after exiting the runway. Passengers were briefed. We then continued to the ramp. Suggestions: I do not have any suggestions at this time.