Take it back and have it checked again, could be anything, from a stone stuck in the back plate etc , a lose heat shield and so on ..it's under warranty, also if wheels where take off have the wheel nuts torque down again.
They still need to provide proof that the modification has caused failure of the part under warranty, it all depends on the dealership I find and who you deal with , but if one is worried about warranty I say don't mod the vehicle.
You said was done by shop ( the lift kit ) did they shave down the strut lower section as required per installation, I ask cos I did the lift on mine on my own and the tolerance is very close when placing the strut back in .
I noticed that is one does not shave the lower strut it will get in...
100% it's about what is important to you , it adds value to how one feels about it , mudflaps do server a purpose as for wheels it can do same , from appearance to performance improvement.
Each to their own I guess .
Cheers
https://rokblokz.com/?gclid=Cj0KCQjw6pOTBhCTARIsAHF23fJxwT9sf1Ysw-QK95J1IIXnf4QWpDEOQSD0xsO0PGfEJmE6iNVjF6waAoqLEALw_wcB
That is the company, I made post with them on here while back.
Trade in , may not get as much but still get a tax break plus don't have to deal with cheap a$$ tire kickers.
Do find out how much it's worth so they don't pull a fast one and lowball you, but definitely less hassle.