Just took the '04 Bonne GXP in to the dealer on Monday (Jan 9). The knock in the steering wheel was caused by a defect in the Intermediate steering shaft. It was replaced under warranty as per a BULLETIN ISSUED BY GM. If any other dealer says otherwise, they're lying. The Bonne is back to her old self again. My dealer was very good servicing the car and caused no trouble about the issue at all.
As a side note, the car has 18,000km (11,000 ish miles) on it at the time of service and has been on the road since April of 2004.