Dreaming a clamp generally refers to problems that are frustrating, they may not be readily understandable, they may be tied with past issues and their solutions do not seem feasible to us. The clamp suggests that what we need is a closure on them so we can move on.
The dream of having a clamp around one’s neck suggests someone feels constraints in what they can say or do and feels oppressed by something or somebody who wants power over them (eclipsing their personality).