Loud humming noise from the back of the car when idle

Question

Last year, after driving a long distance (about 200km), my 2013 Kia Cee'd started making a high pitch humming noise. It was loud when I was stopped but completely drown out by the engine noise as when the car was moving. While driving, the noise could still be heard very faintly with radio and AC off but didn't seem to change with speed or RPM.

The next day, the problem had disappeared. 
Yesterday, I drove again a long distance and the same noise came back. I investigated further and the noise is coming from the back of the car. It can be heard the loudest next to the back wheel wells.

I suspect it might be a small leak in the exhaust but I'm surprised it doesn't get louder with rpm. Does it makes sense that it would only be heard after driving a long distance ? 
What else could make noise around the back when idle in a FWD car ? Should I be worried ?

user4321 · Answer

Since I cant comment I would recommend checking to make sure your exhaust is securely fastened to all of its hangers (thick rubber oval hangers that attach your exhaust to the chassis), the noises especially coming from near the wheel wells indicate either the exhaust is loose or that there might be an exhaust leak somewhere in the system. Do you smell any exhaust before the muffler?

Answered by user4321 on July 21, 2021

Loud humming noise from the back of the car when idle

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