HI,
I normally do not write on this board much. But I recently found (using a Garrett 2500) a metal (copper?) object very similar to what you found in that they both have a similar decorative trim and side hole. MIne was dug out from 1-2 inches of mud from a semi-dried creek bed in a woods that I have found items ranging from 1700s-1890s. I do not think my tube is a whistle because practically all whistles have the end capped or at the very least have a significant narrowing within one end of the tube entrance. However, as you can see in the picture the tube goes clean through with very little narrowing (except the bent part which was not on purpose). This really would not work as a whistle. I thought it could be the mouth piece for a hunting (fox) horn but those do not have holes on their sides. It really is a mystery. I would very much like to know what this is and in what period it was made (1700s or early 1800s or Victorian).
Could you post a picture of the top of the tube to see if there is any significant (and purposeful) narrowing?