A321 Technician acting as brake rider during aircraft tow heard a noise from the result of aircraft making contact with an object.

Narrative

I was the brake rider for Aircraft X. I went through my Ground Handling Power On safety checklist in its entirety. I started by verifying all doors were closed and disarmed as well as the galley and the lavatory areas by physically walking through the aircraft. I proceeded to check the logbook and my emergency briefing guide as normal. I checked the circuit breakers; ensured the parking brake was on and the landing gear handles were down. I verified that the speed brake lever was retracted and disarmed and that the thrust and reverser levers were idle and stowed. I then made sure the wing and anti-ice switches were off. I continued through my checklist and checked that the battery voltage was 25.5 or higher and turned on the battery 1 and 2 switches. I advanced onto the APU start by visually inspecting that the fire switched was in and guarded and checked to see if the agent lights were out. I proceeded onto pressing the APU Fire Test button and once it flashed I turned on the Master Switch button and then the APU Start switch button. I made sure the APU GEN switch button was on and that the light was out and ensured there were no lights on the ventilation panel. I moved onto the rest of my checklist and confirmed that all safety checks were completed. I established APU power and turned the beacon and navigation lights on. I turned on the radio and set the frequency to Operations and Ramp Control. I verified that the cockpit speaker was on. I ensured the ANTI SKID & N/W STRG Switch was on then verified it was present on the ECAM (Electronic Centralized Aircraft Monitor). I pressed the yellow hydraulic pump button and made sure it said 'on.' I checked the Triple Indicator was in the green band. I pressed the Door button and the Press button and verified all doors were closed and that the outflow valve was open. I checked the fuel quantity and turned the transponder on. I proceeded to call Operations; verified the gate and then called Ramp Control to verify the gate and alley was open. After I received clearance; I called down to the comms person and informed them of our gate and that the gate and alley were open. They asked me to release brakes; I waited until the parking brake message disappeared from the ECAM and let the comms person know. They proceeded with the tow. A few moments later; I heard a noise and got back on the radio to ask the comms person what the noise was and they said; 'I don't know; it's probably chalks.' A few seconds later the noise got extremely loud and I asked the comms person was everything ok? They then said they weren't sure and stopped the tow. I asked them if they wanted me to set brakes and they said 'no;' and immediately after said 'yes.' I set the brakes and verified on the ECAM that it said the parking brake was on. A few minutes later; the comms person called me back on the radio and said to shut off the APU because 'something is unhooked/wrong.' I went back to my check list and performed the shutdown procedures: I verified that the parking brake was set again; turned off the yellow electric pump; turned off the beacon and navigation lights and then turned the transponder back to standby. I then doubled checked that ADIRUs were off; the flight deck windows were closed; the emergency lights switch was set to off; and the cockpit interior lights were out. I continued with the shutdown procedures and turned the APU Master switch off and waited two minutes before I turned off the battery. The crew called me on the phone to let me know the aft door was open and that I could exit the aircraft from the rear. I exited the aircraft; closed the door; walked down the stairs; and assisted with removing the stairs from the aircraft. I walked over to the rest of the crew and got in the van.When I exited the aircraft; a few managers were there along with Maintenance.