dc42:
Yes, it does seem strange. I suggest you test the diode that you fitted in the new position. Does the garbage appear when the solenoid turns on, or when it turns off? Also see my previous reply about +5v and ground wires to the LCD. A photo of your wiring would help.
I will do more testing here, and take a photo after I clean up the wiring. The garbage characters appear always when the solenoid is turned off. I am powering the LCD using the 5V and GND pins directly from the Arduino UNO's power rail. Thanks.