Check with your local power companies engineer and see if he can contact the power distributor and request a rfi location team to come out. Also request a bucket truck crew from the local power come out at same time which the rfi team will likely do anyways to fix as they find. Try to schedule on a day that the interference is present. And follow them around, its good education. This was a real break for me as my power company was like yours and did not have much rfi location experience.
The rfi team showed up with a van of equipment including 3 pieces. A shoulder mount variable frequency receiver with small log periodic to locate the pole, an ultrasonic handheld dish receiver to isolate to usually one component, and a ultrasonic stick mounted sniffer for the bucket truck guys to really pinpoint.
I was lucky in that i got a guy (and another younger fellow) at first with the rfi team that was about to retire (unlucky that he is now retired). He wasnt in much of a hurry and stayed 2 days and located -many- sources.
Also look at April 2006 QST for a build your own ultrasonic dish receiver and May 2007 for a antenna to go with your portable receiver and what type receiver to use and other info.
I have about got all the parts to build the ultrasonic and hope to locate a couple of aggravating intermittents popping up lately.
I would strongly suggest you have someone locate the source(s) instead of the hit and miss which might burn out your local power company and cause strained relations (been there done that so i know).
Lastly do searches on the web and do all the reading you can about the topic. Read the ARRL's RFI book and others. My experiences at http://bellsouthpwp.net/a/f/af4o/rfi.html