Power delivery, IEEE Transactions, vol. 17 Issue 2, 2002, "Evaluation of the potential for power line noise to degrade real time differential GPS messages broadcast at 283.5-325 kHz.":

"The new Nationwide Differential Global Positioning System network uses the 283.5-325 kHz band to broadcast differential GPS (DGPS) correction messages. Concern has been expressed that power line corona and gap discharge noise could degrade the performance of DGPS receivers using this band...."

Cutting to the heart, if you are lost, do not use your GPS near a power line.
The article goes on to say that nearby nonpower line RF noise sources also may disrupt performance, such as those in vehicles.

Google the article if you are interested in its content.