Muffler exhaust/engine

I have a 2011 Chevrolet Traverse 152,000. Couple
days ago i felt my engine making a little noise.
Whenever i accelerate the gas pedal it makes a
sound like a racing car then when i hit 40-45 it
stops. So i took it to firestone they said oh it’s your
engine thats normal!!!!!! No its not normal because i
never heard that noise before!!!!! So i took it to a
different mechanic he said its your muffler it has a
very tiny hole on the muffler exhaust,its  fine no
need to change it!!!!! Now my gas starting to get
low after a day and i don’t use it much. Nothing is
leaking from my muffler or exhaust just a little rust
and a tiny hole can this be my issue with my engine
and sounding like a racing car?!!! My engine light
isn’t on either!!