I have an 03 Civic EX automatic with 43k miles (mostly highway miles). I just started noticing that speeds over 30 or 40 mph I'm getting a low hum or vibration sound. It almost sounds like I'm always running in 2nd gear (but not quite as loud). But the car seems to shift OK and its running at the same RPMs it always has at the same speeds. No check engine light has come on. Anyone have any ideas?

 

Is the sound coming from the wheels? If so you wheel bearings might be on thier way out.

 

Is there any warranty left on that? If so, ask the dealer to check it out. They'll hook up a scope and find where it's coming from. I've got a 98 civic and at around 3000 rpm I get that same kind of sound. I thought it was speed related, but it does it in any gear at the same engine speed (under no load). I listened for it at idle and found out it was just an exhaust heat shield. But, I'm not implying that's your problem, just a suggestion. If it's happening in a narrow range of engine rpm, it may be something vibrating. If it's a much wider range, there might be a bigger problem.

 

I don't think its the bearings - its not so much of a rotational sound.

It seems to make the sound between 2000 and 2600 RPMs. I do have a service contract for another 30k, so I think I will take it to the dealer.

 

Agree with agentofdarkness...happened to me in other cars and these were the symptoms...