Why would a Prius make a thump noise & 1 second hesitation once in a while?

motor mount?

 

An undulation in the road?

 

I had that happening for a couple of weeks a few cars back. It always gave this loud thump when I made a quick turn. My bowling ball had come out of its bag in the trunk. I'm guessing that is not your problem, but thanks for bringing back that memory.

 

the loose bowling ball is more common than you may think. some owners aren't even aware that one comes strapped down under the hatch floor with every prius. if those straps come loose...

 

While your question lacks clarity and description, a thump and one second hesitation could be traction control triggering under abrupt acceleration.

Watch the dash for the orange flashing traction control light. It looks like a rear view of a car with an S trailing from each back tire.

EDIT: Sorry, brought back an old thread. I'm new here.

 

no worries, since there hasn't been resolution, you might have hit on it

 

Apology refused, because it isn't that old. It is just single digit months back, quite fresh compared to the multi-year-old threads that others dredge up.

And as Bisco noted, it also wasn't resolved, so new ideas are still quite welcome.