sory, i missed your post.
Rach requests do not contain the BSIC.
Yes, they are GMSK modulated. But that doesn’t allow noise detection. EM Noise could “sound” like a GMSK signal.
Yes, Ghost RACH are rare, if they are just noise. But sometimes, some equipments generates a signal which is exactly containing a sequence of 900MHz phase modulated symbols. In this casse, it is decoded as a RACH.