There were "anecdotal reports of vibration" after soldiers took part in pre-trials training on prototype variants of the Ajax vehicles in 2019.
Jeremy Quin, the Minister for Defence Procurement, was answering a written parliamentary question from Labour MP Kevan Jones, who asked when the Ministry of Defence (MOD) was "first informed of vibration issues identified during Ajax Armoured Vehicle programme trials".
The defence minister replied, stating: "As preparation activity for the Capability Drop 1 vehicles at the end of 2019, some soldiers were invited to do pre-trials training on prototype variants.
"Whilst the on-board sensors did not register any issues subsequently there were anecdotal reports of vibration.
"A small number of soldiers engaged in Entry Qualification Trials reported noise and vibration characteristics in July 2020 and in September 2020 a medical staff report raised possibility of noise injuries.
"As a result, the Authority commissioned in-ear assessments through the Army environmental health team. Evidence from this led to the immediate stop of all dynamic vehicle training on 6 November 2020.
"The Authority has subsequently commissioned independent trials with Millbrook Proving Ground to provide an independent assessment of the vibration data provided by General Dynamics which we expect to report in late July 2021."
Watch: Jeremy Quin gives details on noise and vibration issues with the Ajax project.
The delayed Ajax programme has faced criticism from some defence experts, with the Government admitting troops involved with the testing had raised concerns over noise and vibration levels, with some personnel "receiving ongoing medical attention".
Mr Quin told the House of Commons: "I don't deny that we've got serious issues that we need to resolve."
Trials involving Ajax were paused for several months following the reports of noise and vibrations.
The new vehicles, formerly known as the Scout SV (Specialist Vehicle), are being developed as part of a multi-billion-pound deal with General Dynamics.
Around £3 billion has been spent on the programme so far, with the agreement with General Dynamics for Ajax being a "firm price contract", with £5.5bn "the maximum that is payable, including VAT", according to the Government.
Cover image: MOD.