Buzzing sound coming from under the back end

Buzzing can be an issue with the door lock or central locking mechanism. You could try hunting for where the sound is more accurately. This will sound a bit silly but try this. Sound can travel through solid surfaces so can sound like they are coming from somewhere else. Put your ear against the side of the door panel nearest the handle and lock the car. Your listening to see where the noise is loudest. Listen at the hinge end as well to check if it's actually coming from inside the engine bay rather than inside the door.

Wheel bearing? If you turn left and it gets louder. It is the right wheel bearing. And vice versa.

Does is sound like a loud humming / buzzing sound ? If so it could be the bearing.

Can you describe the sound in more detail? Is it constant ? Does it change if the car is turning to the left or right ?

this sounds like a hub bearing, to determine which one it is when your driving and you here the noise turn the steering wheel slightly left and then slightly right, the noise should get louder or lighter. If louder on right turn then it would be left bearing is bad because your putting more weight on the left side

Sounds like a ball joint, or steering linkage. Jack up the front end so the wheels DO NOT TOUCH the ground and put safety blocks under axle

grabs the wheel with your hands at top and bottom, try to jiggle the wheel, not turn, try to lift, shake up + down. If there is shaking, then it's a balljoint.

If no shake, then you'll simply need a wheel alignment

the buzzing is the relay driven by the daytime running light module.
the module is under the left side of the dash by the fuse box,but above it and more to the middle.right above your left knee about 8 inches or so.

sounds like the fuel pump which is actually in the gas tank but will sound like under the seat if it never made the sound before it might be getting worn out have it checked out

Rather than guess witch one it is( sounds to me to be a wheel bearing or hub bearing) just chg. out both, but if it gets louder when you make a right turn i would say its the left side sense when you make a right turn you are putting more forse and weight on that side.

Sounds like a front wheel bearing. Pretty common. You have to replace the hub as an assembly. No servicable parts inside.

The fuel pump is located inside the fuel tank which is in the rear of the car. It's powered by an electric motor. Check the owner's manual for location of fuses and relays. Some are located under the hood (either on the fender or firewall), others are under the dashboard (near your left foot), on the side of the dashboard (look for cover on side of dashboard with driver's door open) or even inside the glove compartment (if you have one). That sound of a motor running is normal, and may be louder if the tank is close to empty.