Some Roland products feature a grounding screw, usually found at the rear of the product. The reason this is in place, is due to the product either being double insulated, or using a low voltage power supply. Therefore, a safety earth connection is not required.
However, this may sometimes cause a strange tingling, although harmless sensation when touching the casing of the product. The product's user manual usually refers to this, such as the below example.
"Depending on the circumstances of a particular setup, you may experience a discomforting sensation, or perceive that the surface feels gritty to the touch when you touch this device, microphones connected to it, or the metal portions of other objects, such as guitars. This is due to an infinitesimal electrical charge, which is absolutely harmless. However, if you are concerned about this, connect the ground terminal with an external ground. When the unit is grounded, a slight hum may occur, depending on the particulars of your installation."
Connecting the grounding screw in your product may also help with interference, buzzing or humming noises when the product is connected to other equipment. It is worth exploring this as an option when this type of problem is reported.
NOTE: Compliance with safety standards is essential when installing the grounding connection for electrical devices in your country or region. We advise that connecting the grounding screw should only ever be attempted by a competent or professional electrician or engineer as necessary. If you have any doubts or concerns about grounding installation, consult a specialized electrical contractor or a qualified technician. Due to health and safety concerns, Roland cannot offer detailed advice on making this connection.