Knock, knock

I'M PLEASED with the overall performance of my 2004 Ford Territory, but after returning from an extended trip around Australia towing a caravan, I began to hear a knocking noise under the dash, in front of the steering wheel. It sounds like somebody tapping a screwdriver on the plastic dashboard. It only does this when first starting the vehicle on a cold morning, and continues every couple of seconds until the car warms up. I told my dealer about the problem, and they said they would have to remove the dashboard and this would involve a couple of days' labour. As I am a pensioner, I can't afford the charge. Has anybody else had the same problem?