I'm assuming that youre talking about Baltimore County PD's PCT. 9 talkgroup. This might be more suited to the MD forum next time you post. Also, please specify exactly what agency you are referring to and what state/county/system. Your original post leaves alot to the imagination.
Be sure to check your status bit trunking codes to see if they are enabled. If memory serves Pct. 9 and Pct. 8 regularly patch their dispatch groups together. Also try 1840 and see if you can hear both precinct's traffic on that group instead of the usual 1872.