This may be totally unrelated except for the symptoms....
I once had an abandoned, but still connected inter-building cable that got damp. The moisture and slight movements from wind were momentarily shorting one pair (an SLT port in this case) and the KSU interpreted it as dial pulse dialing. The random 'dialing' made several calls to 911. Also made a bunch of internal calls to 211, 311, 212, etc. Mostly the lower numbered digits.
I spotted random off-hook activity on ports that should have been idle and that led to isolating/eliminating the cable.
