whenever i back my car up and brake, i hear a knocking noise coming from either the engine bay or the passenger side wheel well. i all my motor mounts and tranny mounts checked and none were bad.
another annoying sound comes on when i start the car. after the engine turns over there is this weird electronic sounding hum that comes on and then shortly turns off.

anyone have any idea what is causing these odd sounds, i just want to make sure nothing is wrong with the car.

 

the knocking noise could be coming from your brakes. there could be some play in your brake pads and i think that the humming is your fuel pump pressurizing the lines. Mine make the same sound.

 

Im not sure about the knocking sound, but I get the same electronic whine sound as well.
I had a knocking sound in my engine bay too and I thought it was the motor but I had Honda check it out and it turns out it was someting broken with my AC pulley system or something so they just cut it off.

 

im guessing not but is your abs light on? sometimes if the abs motor is bad or going bad it will make an anooying sound for the first few seconds when you start it up. otherwise when you first start the car the fuel pump does pressurize the lines like Keats97turboteg said. but anyways good luck.