[NefCanuck]

Have you checked out the Tarion New Home Warranty information?

Here is their website:

Tarion New Home warranty homepage

Since your past the builders warranty at two years you're into the Tarion seven year coverage which covers:

A major structural defect is defined in the The Ontario New Home Warranties Plan Act as:

Any defect in work or materials that results in the failure of a load-bearing part of the home’sstructure or materially and adversely affects its load-bearing function;

or

Any defect in work or materials that materially and adversely affects the use of the building as a home.

I'm not sure that what you're experiencing falls into the second category, but it doesn't hurt to try (you may need an engineers report to back up the assertion that the floor was installed too tightly)

NefCanuck