My friend has borrowed my car for a few months (2004 A4 Audi V6), yesterday she told me that her other friend rear-ended her "very lightly", after which the car exhaust started making a weird noise. She says she didn't feel any impact but heard the collision. The bumper (from what they say) was not touched.

They took it to a mechanic who is a mutual friend of theirs, and he stated that the issue is that the flex-pipe shattered from impact due to old age, quoting the repair at $300. He also suggested not going to the dealership which would charge thousands for replacing the entire exhaust system (I'm well aware of dealerships overcharging but I want to make sure the friend is not hiding a several-thousand dollar repair with a temporary $300 fix).

The friend said he would pay for the repair and wants to avoid involving the insurance. I'm not against it, but I want to make sure I fully understand the problem myself and that there are no additional issues I would encounter later due to said friend of a friend cutting corners.

Since I'm unable to see the car until tomorrow, and therefore can't post photos, what should I look for as signs of further damage? Does this repair/problem from a minor rear-end collision sound reasonable to you? What else do you expect to get damaged during such collision?

A few things concern me:

• I've been rear-ended before and I have bumped another car before, I know that bumper is the first to be hit and the first to scratch or crack, the fact that it wasn't affected seems odd to me
• I also have typically "felt" the impact before "hearing" it, which makes me wonder how light it really was
• This friend has also racked up over a hundred dollars of toll fees without telling me in the past (although she paid it after I showed her the toll readings), which is what makes me suspicious to begin with, I don't know if she's telling me the full story
  

I'm considering having an independent mechanic look at it, but I don't want to be driving the car around in this state or being difficult to my friend and this mechanic who is doing them a favor by charging less for the repair.