Seismic G5 Spring Trucks were engineered as a high-precision product, with virtually no slop in their steering articulation. So like a race car, they don’t dampen road vibrations much and may seem noisy compared to lower-precision trucks that use bushings. Some skaters are more sensitive to that than others.
Actual rattling noises can occur for a variety of reasons, regardless of the trucks you’re using. The most common cause is riding on rough surfaces with loose hardware, no shock pads under the trucks, and/or wheels that are too hard for the surface. In addition, bearing spacers can rattle between the bearings or against the axles if they’re the wrong size, or if the wheel core tolerances are off.
Try using softer wheels with properly-spaced bearings, and truck risers made of urethane or hard rubber. Also check the fastening tension of your mounting hardware, wheel nuts, and truck pivot bolts. (Loose pivot bolts can also invite dirt and grime to gunk up the works, which in turn can lead to excess friction among the moving parts.)
The Seismic G5 technology itself was carefully engineered to eliminate squeaking, clicking and rattling, but a few seldom-seen issues can lead to these or other noises.
Most squeaking and clicking stems from friction between the small inner springs, the main outer springs, and the long-necked “sliding” spring caps. To reduce or eliminate the noise, try rotating the spring assemblies a quarter or half turn inside the spring chambers. (Loosen the tension screws first, then just turn the springs with your fingers.) After that, tighten the tension screws at least 1.5 turns. For added measure, drop a bit of silicone or graphite lubricant inside the long spring caps.
Finally, spring tension screws that are fully loosened may occasionally rattle inside the Seismic truck hangers, though ordinarily spring pressure keeps them quite still. Try tightening them 1.5 turns. This puts them in a “neutral” position where they function as intended. The trucks won’t feel stiffer when riding, but pressure from the springs will keep the screws from rattling.