afro – you’re right, i answered a little quick.
focusing on a BTS issue makes more sense.
the problem is happening on all the cells of the BTS ?
are you able to see the impacts on KPIs such as call drops, tch assignments failures, sdcch drops, sdcch assignments failures ?
have you checked the path balance ?
please do so on each TRX if possible.
A good investigation method is to lock all trx and unlock only one at a time, in order to perform call test.
if there is a mixed feeders, the TX of some TRX might be transmitted to the antenna of the other sector, etc… that might cause very poor call quality when the call is assigned on those TRX.