You could perform some Abis interface traces, to isolate those “funky” Channel Requests. My guess is that an external interferer is generating a certain sequence of bits. These bits are decoded by the BTS as being “emergency call”, at a TA=16.
Other possibility : the BTS itself generates this noise.
Could you check when are those RACH transmitted, and how often ?
Try changing the BCCH frequency to a frequency far away (2 or 3 MHz away) (for few hours, or one day, only), and see if the problem is still there. If yes, then the problem might come from BTS, because if it was from an external interference, it would not be heard on other frequencies (otherwise, other BTS’s would hear it as well)