Q: My 2007 Avalanche is making this click ticking sound when I drive in the D position when I'm slowing down I drove it the other day

What you are describing sounds like a failing CV joint. A CV (Constant Velocity) joint is a shaft that connects the transmission to the wheels, essentially transferring the power from the drive train directly to the wheels. The CV joint is packed with a special grease and sealed tight with the rubber or plastic boot, that is held in place with two clamps. The most common problem with the CV joints is when the protective boot cracks or gets damaged. Once this happens, the grease comes out and moisture and dirt get in, causing the CV joint to wear faster and eventually fail due to lack of lubrication and corrosion. When the CV joint becomes damaged or worn, you may hear a clicking, clunking or popping sound coming from this area as the weight of the vehicle puts pressure on this area and shifts back and forth and side to side. I would recommend having an expert from YourMechanic come to your location to diagnose and inspect your vehicle.