I have lost nav in a B727 twice when both units failed. I was able to continue but on a MIA to CUN flight had no long range Nav. When the passengers deplaned and baggage was unloaded everything worked perfectly again. It could have been an FM radio in baggage that turned on with an alarm or a cell phone.
I worked on business radio systems before flying full time and had some interesting situations, one when a weather receiver was jamming one of our companies radios in their office on a UHF frequency. I tuned to our frequency and drove the jeep around with a scope tuned to that frequency and it peaked out passing a business trailer. I stopped and verified their receiver was sending harmonics out of the antenna of their receive only unit and causing the problem. Also at KSNA we had a constant problem of clearance delivery having a loud squeal when they were reading clearances. I took a portable radio tuned to the frequency and it was our Aircal high speed printer in ops sending out the signal. We dealt with these interference problems a lot and they sometimes are not very straight forward solutions. Now with GPS and being familiar with your wet compass it shouldn't cause much of a problem if you can think outside the box a little.