start with looking for uneven wear on tyres around the circumference and not accross the width you could be suffering from cupping, it was an issue with early bridgestones when the zed was first released. Your cheap tyre may have the same issue. Tyre pattern was redesigned on the Bridgestones and Nissan replaced the tyres.
Feathering/Cupping
These terms are used to refer to a specific type of undesirable front tyre wear on some 350zs. This problem occurred for many (but not a majority) of owners in the US and has been found in the UK as well.
The tyres wear unevenly on their outer (check) edge leading to roaring/rumbling/howling noise which gets worse as wear/mileage increases. Some owners have reported associated steering feel changes and even reduced front end grip.
Nissan GB now recognise that this condition can occur and will inspect tyres when the problem is reported. If they find that the problem is affecting a car, they will usually replace the tyres and reset the toe-in settings of the car to avoid the problem re-curring.