Loud engine?

My girlfriend has a 06 explorer and sometimes when leaving from a stop the motor sounds real loud like its geared super low or somthing anyone know what this could be ? it shifts fine just sounds like a semi coming down the road

Maybe a hole in the exhaust .. maybe a loose exhaust manifold.

its not exhaust loud its just sounds like the RPMS are through the roof but they are not sounds like the fan is going 20,000 rpm's if u know what i mean

check your coolant level...fan will engage tighter if motor starts getting a little warm after idle at stop light

My wifes 07 was doing the same thing after she had the oil changed. I popped the hood and the jerks @ the dealership did not put the air filter lid on tight. I put it back on and it was fixed

not sure if you fixed this by now but the problem sounds a lot like the seized fan clutch I had on my 99 OHV. I'm not sure if the SOHC has a fan clutch like mine did but when that thing seized it was loud as hell. I got a new one from autozone(w/lifetime warranty) and that fixed it.