Getting a sound that i cant quit explain other than a race car exhaust sound, but its weird, happens alot when i take my foot off the acceleration and seems even worse in sport mode. One mechanic jacked it up and looked under it, hit the 2nd stage exhaust and heard a little ding, and said something inside is loose or bad says it needs to be replaced, but im not too sure about that being the source of the noise. anyone have an idea?

In the video, youll hear the exhaust i guess be a bit loud however the sound im speaking of you will notice the variation.

0:38 You'll hear the variation. it was only brief this time, but i get that for longer periods at a time.
and 1:05


Video

just want to know if anyone has experienced this and if the Cat converter can cause something like this, not looking forward to unnecessary work at the mechanic.

Audi A6 2006 Sedan 3.2