Clicking noise coming from rear
Pinnacle is Evans Cycles' house brand. Evans offers a free "6-week" check up with all new bikes. Ensure they note the spoke tension problem on the worksheet when you book the bike in.

When wheels are built, the spokes can hold a smooth curve through a crossing point, especially with thicker plain-gauge (unbutted) spokes, rather than forming a kink at the crossing point. With normal "J-bend" spokes, the bend at the elbow may keep its original 90 degree angle and prevent the head from settling properly in the hub drillings. Over time, this bend may tighten or loosen (depending whether it passes through the hub flange outwards or inwards) until the head is properly flat against the face of the hub flange. Both of these stresses may settle over time causing spoke tension to be lost. Experienced wheelbuilders will attempt to relieve most of this stress before finally ensuring the wheel remains true and has the correct tension.

Another cause of tension-loss with lighter butted spokes is wind-up, whereby as the tension is increased during the build, friction between the spoke threads and nipple threads can prevent the nipple from screwing further onto the spoke, causing the body of the spoke to twist instead. As the wheel is used, the twist-tension of wind up can release itself by unscrewing the spoke from the nipple or by spinning the nipple within the rim. Wind-up can be limited by using proper lubrication at the nipple threads and where the nipple sits in the rim, and by using brass washers between the nipple and rim (especially with a rim that doesn't have eyelets). When choosing lighter spokes, a bladed spoke (such as the Sapim CX-ray) allows the wheelbuilder to see wind-up and prevent it by holding the flat section of the spoke.