There are way too many 'ripples' in that bumper, lol

 

actually, no, that's the reflection causing a rippling effect in the paint. as for the excessive movement while in reverse, it's probable, but i've never checked it while i was backing up unless i were to jump out at some point with the car still in motion.

 

haha, im gonna have a friend watch it while I back up then. At least it's not a metal noise so I guess thats good and at least the noise is gone since I trimmed the lip...
Could it be anything else aside from the lip?

 

could it be the exhaust hangers are too soft?
Would upgrading to something stiffer help?
Doesn't the exhaust need to vibrate?
Anything wrong with it vibrating too much or too little?

 

if you solid mount your exhaust, it's like installing an engine damper, your ride comfort will go down. that's why everything is rubber mounted such as engine mounts, top mounts, etc.

 

turns out the problem was it was still knocking on my rear lip. When I manually shook the exhaust, i just shook the exhaust tip... but today i realized the whole muffler vibrated and I trimmed a little more of the lip away and it works!!!
I'm still gonna keep the stock rubber hangers though.
I guess its okay for the exhaust to vibrate that much?
Either way thanks