Two problems related to frame rust have been reported for the 2003 Nissan Altima. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2003 Nissan Altima based on all problems reported for the 2003 Altima.
Had to replace front passenger floor pan because there was a hole about 15 inches long and 5 inches wide due to rust. My front subframe is completely rusted at this point. Rust is expected in new york due to salt, but after talking with Nissan they said they have not heard anyone else having issues despite thousands of hits on a simple internet search about rust issues for Nissans.
The contact owns a 2003 Nissan Altima. The contact stated that something was protruding from the under the vehicle. The vehicle was taken to an independent mechanic where the contact was informed that the frame was rusted and bore a hole on the passenger's side of the vehicle. The vehicle was not repaired. The manufacturer was notified of the failure. The VIN was unavailable. The failure and current mileage was 120,000.