[Tools]

If the watch is fully wound, I might think that you could feel the mainspring as it slips from one "notch" to another inside the barrel.

The mainspring is friction fit inside of it's barrel. There is a tang that presses outward against the inside lip of the barrel along with some machined notches that gives it places to push against.

When everything is new, those notches have crisp edges. As the watch ages or it keeps getting overwound and the mainspring has been slipping a lot, those notches get rounded out. When this happens the mainspring won't be able to maintain a full wind and the barrel needs to be replaced.

The mainspring coil also slips against itself when winding to balance out as it tightens.

Not saying that this is absolutely what you are experiencing, it's just something unique with a mainspring wound watch.