When the Z-axis of the U1 moves to around 190 and then continues downward, a strange noise occurs, resembling a friction sound, which can be heard every time after printing when moving downward. I found that this noise is caused by the heated bed cable rubbing against the casing.
The solution is to apply a layer of Teflon tape along the edge, as the tape has a self-lubricating effect, which eliminates the friction noise.
The result is as follows:

After testing repeated up-and-down movements of the Z-axis, the abnormal noise has disappeared.