Looseness in the steering shaft and steering shaft coupling U-joint can cause a knocking / popping noise from the steering column when turning. The steering shaft and coupling U-joint will need to be replaced.Google+
Car Problem Reports
Mercury Mariner Knock/Pop Noise from the Steering Column when Turning
Mercury Mariner Problem
Average Mileage: 92,896 mi (54,500 mi - 170,000 mi)
Visitor, 2008 Mercury Mariner, 77,000 mi
popping and vibration during steering maneuvers - local Ford dealer quoted $1,200(labor and parts)to replace worn U-bolts, and perform necessary alignment.
This has been happening for some time now. I first noticed it last year. There is a knocking noise in the steering column when I turn tight radius was sometimes. I didn't realize this could be dangerous! Now that there is a recall for power steering issues in 2008 - 2012 models it sounds like they should be extending this recall to 2006 models too!
Visitor, 2008 Mercury Mariner, 89,000 mi
just pops and shakes
Visitor, 2008 Mercury Mariner
When making a sharp turn my steering wheel made this popping noise..it pop once..the steering was fine but I am worried that it my be a serious issue
Visitor, 2008 Mercury Mariner, 58,000 mi
Replace steering shaft and u joint. Known issue with Ford as they have newer part numbers that supersede the old ones.
Visitor, 2008 Mercury Mariner, 54,500 mi
Haven't fixed this problem yet. Just started yesterday. Just purchased this car 5 weeks ago used.
Visitor, 2008 Mercury Mariner, 88,365 mi
Found the U-joint bad, took it to the dealer for repair. Ford has to have more Quality and Reliability to their cars. Repairs today are costly in this economy.