I have a 2012 RX that emits an odd sound when shifting in reverse (been doing this for a while). It only happens the first time I shift from a cold start and literally sounds like a person tapping a pair of claves (wooden percussion sticks) together one time. If I put the car in park and shift again, the sound doesn't reoccur. At first, I thought it was the brakes slipping, but I ruled that out. I checked the two visible motor mounts and they look good (thinking something is shifting when torque is applied). Before I go any further, does anyone have an idea what could be causing this?

 

Could be the transmission's internal clutches grabbing during the initial shift into reverse. If you have never done an ATF drain-and-fill, that would be my first step towards resolving this issue. ATF breaks down over time and heat cycles.

 

I had the local Toyota dealership flush the transmission. The clunking is still there but seems less frequent. I did hear it clunk the other day when shifting from drive to reverse (engine warm), but today it didn't make a sound when shifting into reverse (engine cold). The dealership didn't hear anything either when testing after the flush.

 

How did you confirm not brakes? Lube the slider pins and pad contact points? Springs in place? Parking brake sometimes binds... did you try it without setting parking brake overnight? Disregard if you already tried this, but we don't know what you know.

 

Did they look at the engine and transmission mounts? You did not state your mileage, but one or more of them could be wearing out. Same with a rear trailing arm bushing.

 

I recently did a brake job on the car (myself) using new OEM rotors, pads, clips, pins, etc. so I can attest that the brakes are in good shape. The car is parked in a garage at night, so no parking brake needed. As far as confirming not the brakes, I started the car in the morning and pressed on the brake pad as hard as I could before shifting. The car didn't jolt, but something in the right front clunked.

My car just turned 129K. I originally thought it was a broken engine mount and checked the three I could see without removing the plastic covers. Didn't think about the transmission mounts -- will look this weekend. Will also look at the arm bushing.