Frequency clash is when you have same MAIO runing on different radios of same site for 1×1. of same BCCH.
Or the BCCH is same as that of the imidiate neighnbour or in any other SFH or fixed frequency when newarby or same cell is using the same frequency.
Also check combiner port/ Cabinet slot / connecting cables.
Also if more than one TRX of the same cell is having issue check for combiner. it might be faulty