It's an unknown phenomenon.
When we drive on Tokai-Hokuriku exp.way(東海北陸自動車道),
our car's antena starts to beat the ski carrier.
It always occurs on the area just before Ichinomiya junction,
and never occurs on any other area.
It never occurs the opposite side (for Toyama) of the same area.
It seems not depends on the weather.
I searched on Google, but I can't find any relational articles.