Some victims believe it was gunfire.
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The victims say it happened while driving on Highway 152.
Hundreds of people use Pacheco Pass to get to and from work every day. Now after these attacks some are scared to drive on it again.
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Officers are looking through all the reports to see if there are clues that could lead to an arrest.
"I didn't know if someone was shooting or what's going on," says Sidney Rayonez.
For 20 years, Rayonez has used the same route.
He leaves Los Banos around 9 p.m. and uses Pacheco Pass to get to his job in Milpitas.
He's never had a problem, until his commute took a turn for the worse on Wednesday night near Dinosaur Point.
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He describes what he heard as something "like a bang, then a whistling through the window".
"I got to Casa Fruta and opened my door and noticed my mirror was blown apart, and there's a hole in the window."
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Rayonez believes someone may have shot at his car, and says a handful of drivers were also parked alongside the road checking their own vehicles.
Several other drivers told our sister station, Action News, they were a victim, sharing pictures of their damaged cars and adding that it happened while on Highway 152.
California Highway Patrol Officers for the Hollister Gilroy division add they they've received several similar reports of someone throwing something at cars, dating back to the middle of last year.
"We've been patrolling more in that area, especially in the indicated times. Our officers are aware of this, and we're going to do ongoing investigations concerning this matter," said Sgt. Robert Maclean.
Officer Shannon Stiers with the Los Banos division says they haven't received any reports, but plan to be more vigilant while patrolling Pacheco Pass.
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"It is an alarming deal. Something like this is something serious. We take it seriously. If anyone has information, come forward. Let us know," said Stiers.
Rayonez, like thousands of others, will still have to use the highway to get to work.
He's now worried to drive on the route he's used for years.
Officers say another challenge is that these incidents are primarily happening at night.
They haven't been able to get a good description of the suspect, and there haven't been many witnesses.
All the suspect information they have is that the person may be a thin, white adult man with shoulder length hair.