Five soldiers involved in the Ajax armoured vehicle programme have been medically discharged or downgraded.
Both noise and vibrations have been previously highlighted as "two primary concerns" for the Ministry of Defence (MOD) regarding the vehicle, issues which manufacturer General Dynamics said have been "a feature of the design since 2010".
General Dynamics is working to a contract worth up to £5.5bn to provide the UK military with the vehicles.
The Government has previously stated "anecdotal reports of vibration" were made after soldiers took part in pre-trials training on prototype variants of the Ajax vehicles in 2019.
Defence minister Jeremy Quin said those in the military who have been medically discharged or downgraded include cases where hearing loss is "a major or minor cause".
"In the case of hearing loss being identified Ajax may or may not be confirmed as a contributory factor," he added.
A defence source said: "The Defence Secretary has continued to put pressure on General Dynamics to fix the problems.
"While our focus remains on working with General Dynamics for its delivery, the welfare of our personnel comes first.
"The Secretary of State will not accept a vehicle that is not fit for purpose."
As of September 2021, 310 people have been exposed to Ajax noise and vibration, according to the MOD, including 11 civilians plus 10 people who are now veterans.
Watch: What's happened with the Ajax programme so far.
Two hundred and seventy people have been assessed regarding noise issues with Ajax – 231 of those having "returned to duty having maintained or returned to pre-exposure levels of hearing".
Of those 231, 166 people are receiving "enhanced hearing surveillance".
Thirty-four of the remaining 39 individuals to have been assessed remain under specialist outpatient care in hospital.
A remaining five individuals have been medically downgraded (potentially requiring a change of duties within the Armed Forces) or discharged, either for reasons unrelated to hearing or with hearing loss as a major or minor cause.
Regarding vibration issues with Ajax, 310 people have been offered an assessment, which 125 individuals have declined.
Forty-five people have been referred for "specialist assessment" relating to "associated hand-transmitted vibration", nine for "specialist assessment of symptoms which could be associated with whole-body vibration", and nine referred for both.
"None of the individuals exposed to Ajax have had a change in medical grading or been medically discharged due to vibration," Mr Quin added.