Mobile X-ray Vans Hit the Streets

What's in my car that I don't want the FBI to notice? If I had a drug stash, I suppose I'd be upset if the FBI grabbed it. But otherwise, would I even know that they had looked? If the FBI X-rayed my car, found nothing to investigate and moved on, has my privacy been violated? If there's no prosecution or actual disruption of my life, such as a traffic stop, has the Constitution been violated?

I'm sure most people would say that it's still a violation, but if you don't know about it, and there's no arrest, how does it get before the courts? Does the ACLU have standing to inspect the government's records for potential clients?