Well, if sounded like high tension lines then it could have been similar. Those make the buzzing, crackling sound from the corona.
I somewhat doubt it was an eminent lightning strike per say but rather just driving through the storm created a static build-up on the antenna. This is why some antennas are designed to be DC grounded, to dissipate static. I don't remember if your Larsen NMO150 is designed to be at ground potential or not.
Could also be the mag mount, which certainly does isolate the antenna from the truck body electrically, forcing the DC ground to happen through the radio. This is another reason why a solid NMO mount in sheet metal is preferred, no static build-up. :-)
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