Any coil, when power is removed from it, produces high voltage called 'counter EMF'. This Electromotive Force (voltage) happens when the magnetism collapses back into the coil windings. (It's also the reason why your ignition coil produces spark when the points OPEN.) It is momentary like a 'shot' of power and only happens when you electrically release the relay.
I've never heard of anyone complain about this in any car over many decades. Regardless, we have ways of snubbing this high voltage.
Get a common diode, like a 1N4004 (general purpose, one amp) and connect it backwards across the relay coil. More specifically, between the short 'B' wire (that comes from the regulator) screw connection, to the Blue-Yellow wire screw connection.
If you need to extend the wires on the diode, use small 'hookup wire' of any kind. You can solder or crimp the wires to the diode.
Diodes come with a band to show polarity. That band needs to be connected to the POS (B) terminal. - Dave