I have an Accord with 223,000 miles on it. Yesterday, I put it in reverse, started to back up, and heard/felt a loud thump. I thought I had hit something! I put it in park, then reverse again, heard the thump again, but was able to put it in drive and proceed normally. I hear a whine as it shifted through each forward gear, but even that stopped after a few miles.

This has never happened before!! What's going on???

 

Have you have a trans flush? Can be a motor mount when it goes "Thump".

 

going with motor mount