Second Stage Not Properly Attached

[Clark8]

When I launch my rocket, the second stage starts flailing randomly but is still attached to the decoupler. I am using the TR-38-D decoupler. 

How would I fix this and is there any known reason for this happening so I can avoid it from now on?

[Benjamin Kerman]

Screenshots, screenshots, screenshots! If we don't know what's happening and what it looks like, we can't help you. 

One idea: Long rockets can get "wet noodle" syndrome (I.e. Flailing around like a noodle, per the name) 

Fix: Moar struts (auto or otherwise)

[bewing]

We're going to need pix and a craft file. "Flailing randomly" is quite poetic, but we need some harder data than that to diagnose it.

 

[Draalo]

Is the decoupler attached to a heatshield?

If so - go into the VAB, grab the decoupler and remove it. Is the rest of the stage still attached to the heatshield?

(Heatshields do have 2 attach nodes - maybe its connected to the wrong one)

In all other cases: pictures, pictures, pictures ...