I have an E320. When I put the key in it sometimes makes a loud noise and won't turn to start. Then I take it out, reinsert it after turning it the other way...it just makes the normal click, turns and starts. Would this be a problem with the key or the ignition system? Has anyone experienced a similar problem? Thanks for your input!

 

Looks like it was a problem with my key. I took the batteries out and put them back in and the noise and mal functioning stopped. The batteries probably weren't making good contact. A nice inexpensive fix!