I've had my c5 for about 4 months now. No major issues to date but the other day I in a parking lot and passed a space to park in. As normal, I put it in reverse, turned slightly and gave it a bit more gas than I would just backing out of my garage. Well, I felt a grinding vibration from the rear that I had not noticed before. I thought maybe because I had the wheels turned that may have caused it.

Now so far, backing out of my garage or a parking space any other time, nothing, and everything seems normal. Which is how I reverse 99% of the time. It's only when I it give more than a normal tap on the gas that it does this. I would say I've experienced this only 3 or 4 times now.

Yesterday I tried backing down the street in a straight line for about 50ft or so while giving it gas, that's when I feel the grinding, I even felt a pop like it popped into gear hard half way through the test.

I've had the tranny serviced / fluid changed about 6 weeks ago, but couldn't tell you if it was doing this before then. I only drive it on the weekends and the wife will take it to work once in awhile.

I haven't checked for any codes yet but I don't think I'll find anything. Mileage is at 53k and everything has be serviced and up to date after I bought it and was kept that way prior to buying it.

I do intend to have it looked at, just couldn't find anything in the search that related to automatic transmissions.