Ever thought how loud the road noise is coming from the back of your S14? There is a very good reason for this: when Nissan were thinking of ways to save money on this car, they discovered two massive gaps they could avoid soundproofing. By dealing with these, the amount of road noise is quite dramatically reduced.
You need to access the void above the rear wheel arches. To do this, the back seat need removing. You will need 10, 12 and 14mm sockets and a flat-head screwdriver.
In addition, you will need to buy some loft insulation and packaging tape. The best sort is is in a plastic liner, to avoid touching the fibreglass and getting it everywhere (Figure 1). You can pick up a 10 metre roll most DIY stores.
First, release the seat back and undo the four 10mm bolts holding it to the hinge mounting (Figure 2).
Remove the seat back completely (Figure 3).
At the base of the back seat are two grey plastic covers. Carefully remove these with the screwdriver (Figure 4). Undo the 12mm bolts.
Remove the seat bottom completely (Figure 5).
Carefully remove one side trim panel. It is held on by poppers around the front edge, one locking popper at the back edge and the hinged mount (14mm bolt). You will now see the area that needs dealing with. A positive resonance chamber! (Figure 6).
Cut the insulation into two 1.5 metre lengths. Seal the plastic liner with packaging tape. Roll insulation and pack it into the void as in Figure 7. Make sure it fills the space well if not, add more. You can now put the trim panel back. Beware at this point that there are three mounting points on the trim that slide onto the three poppers marked in red on Figure 7. You may find it easier to remove these first and put them on the trim before fitting it. Unfortunately, they aren't easy to remove. Now repeat for the other trim.
When done, fit the seat bottom, then the top.
Hey presto! Enjoy the silence!