Car sounds like I've got a lawnmower in the trunk

I am pretty sure it’s coming from the back of my car but hard to tell. I first heard it yesterday but I though it was an actual lawnmower, I was just pulling into my parking spot and then turned off the car. I drove twice more that night, no sound. No sounds this morning on my way to work. On my way home I heard it again. Again, I thought it was actually someone mowing their lawn as it sounds like it gets closer and further away-sounding just like a lawnmower. I was waiting for a train to pass so I ended up turning off my car to investigate the sound and sure enough, it stopped. I turned my car back on and the sound started up again. It does not change with accelerating, braking, or idling and then about 10 minutes further into my drive it stopped again. 2004 Pontiac Sunfire

Thanks for any advice!

Could be the fuel pump giving up the ghost.


Intermittent exhaust system leak is another possibility

Hanger for muff maybe broke and muff is rumbling on suspension. Or exhaust pipe. I am sure a muff shop will tell you whats wrong

Will check that, tnx.