Occasional crunch/grind from rear when reversing
 

Hi guys,

Over the last month, since the last track day, I noticed that on occasion, when reversing there is a grinding/crunching sound coming from the rear of the car.

It always start reversing fine, but about 1 of 4 times at sound point a sounds like running over plastic bottles appears and persists until I come to a stop. Does not noticeably vary with speed, though it's hard to judge when you're going 0-5kph. Car is fully in gear, reversing at idle.

I'd like to get a video up, but I can't seem to reproduce this on command, it just happens sometimes.

My main concern is that there isn't diff damage, so does this sound like any diff issues anyone has encountered?

Other than that the car behaves normally.

Thanks!

Car is a 2004 6mt. Redline fluids in trans (MT-90) and diff (75w90 no additives) are fresh from April.

do you feel anything on the brake pedal when this happens?

I'll have to check, I'm not on the brakes when it happens.

However, I did find a way to reproduce it pretty consistently: it happens when reversing while turned. Going straight it doesn't usually happen.

Thinking the suspension might be loose or binding somewhere, so will examine that next.