My girlfriend has an 03 civic wiht 70k that has a really loud hum coming from the rear end increasing/decreasing with speed. She never even noticed it (women[:@]) Its obviously nothing with the drive line, is there anything that commonly goes bad back there that would cause this hum? Thanks.

 

loud hum.. probly not a muffler problem if you cant here it when you rev the motor?
You here it only when driving?

 

If it is related only to car spped, could be a wheel bearing. Jack up the wheels one at a time to see if they turn smooth and quiet by hand. Any noise at all from the bearing during this test is bad, it will get a lot louder with the weight of the car on it.

 

thats my bet too, going to try it out tomorrow. easy fix or a bear that needs to be done by a mech?

 

Try rotating your tires,maybe your alignment is little off thus causing uneven wear on your tires. When this happens, you can have excess tires noise.