A squeak from the steering column is often related to a rubber boot in the column or a seal in the power steering rack.
Car Problem Reports
Mercedes-Benz E430 4MATIC Squeak in Steering Column Due to Rubber Boot or Seal
Mercedes-Benz E430 4MATIC Problem
Average Mileage: 62,500 mi (25,000 mi - 100,000 mi)
annoying, can hear engine noises more as well as firewall sound deadening is diminished.
Visitor, 2001 Mercedes-Benz E430 4MATIC, 25,000 mi
The dealer changed this rubber boot and the entire steering gear under warranty. They said it was out of spec, but I doubt it. The rubber boot still squeaks occasionally and I ignore it. A squirt of silicone would quiet it. I have 130,000 miles on my car and am very happy with it.