Muffin, it might be your proximity to the TNT VOR which brings the big birds over you. All the Chinnooks I see in that area appear to keep over that part of the Peak. Maybe part of a noise abatement/ training route?
Surprised that they would not have TCAS? Many twins have TCAS fitted so why not large military helis, as they are most likely to bump into low level VFR traffic outside CAS?
h-r