بسم الله الرحمن الرحيم
It is lawful to do zikr loudly in the mosque or in the outer portion of the mosque. However, doing zikr loudly in a way that causes disturbance for others is not correct. Such person should select such a place in the mosque where others are not disturbed if he does zikr.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.