If there's a high pitched noise, then the power supply is probably running ok but under excessive load from a fault in the line output circuit. Usually a sign of a short circuit line output transistor (inexpensive) or line output transformer (expensive). More common is transistor though. Contact manufacturer re warranty, they should have records to verify date of manufacture against it's serial number and date of sale to the dealer, irrespective of warranty card and dealer should have record of sale to you. Really shouldn't be a problem, don't let them fob you off.
Cobweb, June 2005