Several black helicopters of various types just went by – one was that kind of heli with a jet engine that the military uses; others were conventional ones. It sounded as if they were flying very low. As they went by, I heard a spray of something hit the roof.
Do those jet helis leave a contrail like planes do? If they are flying low enough, could this particulate stuff actually hit your roof before dispersing?
A turbine engine. Sounds more likely it was dust and dirt stirred up that hit your house, if they were involved at all, that would be awfully low. It’s not a jet exhaust producing thrust, so a contrail wouldn’t normally appear except in ideal humidity conditions, and then it’s not really the same as a jet engine contrail.
Unless the helicopter was shedding parts or streaming fuel you were hearing things.
Contrails are composed of water, typically ice at high altitudes. At ground level, this is known as “fog”. I have no idea what “particulate matter” you are talking about.
Just so you know, the “Men In Black” don’t use black helicopters anymore to disappear people. Everybody knows about black helicopters. They use red ones with yellow racing stripes on the side or blue ones with white stripes. They have removable decals on the sides with the logos\call letters of local TV and Radio stations. That way no one will suspect them. 
There is not really such a thing as a ‘jet helicopter’. All large-ish helos, military or civilian, use turbine engines (sometimes called a turbo-shaft). It does not push the helo forward with jet exhaust like a true jet aircraft, it just uses a turbine engine instead of a regular reciprocating internal combustion engine to rotate a drive shaft which spins the rotor.
The reason all but the smallest helicopters use turbine engines is they have much higher power to weight ratios than piston engines, run smoother and much more reliably, all of which are crucial for helos.
Well, I guess that’s the last we will be hearing from brujaja. 