Hyundai Repair: sonata 1998 rattles when coasting and driving, wheel hub, cv joint

Question
I have a four cylinder. when driving at normal to medium speeds there is a knocking sound that you can feel through the floor. When sitting at idle there is no sound even if you rev the engine. It has brand new tires and brakes. A coworker suggested CV joint but Advance Auto doesn't agree. They say the joints would only rattle when turning. There is no sound when braking. Any ideas?

Answer
Since this occurs only when the vehicle is moving, the problem lies somewhere with the transmission, axles, or the components attached to your wheel hub.  To find out for certain where the noise is originating, you'll probably need to run the vehicle on a lift so you'll be able to be underneath the vehicle to find the source of the noise.  

While there could be something broken in a CV joint causing this noise, this type of failure is very rare.  Most likely, it isn't a problem with the CV joint itself, but listening to the car on a lift as suggested above will help you determine whether that's the case.

I understand that you probably do not have a lift at your disposal.  In that case, you'll probably need to have a local shop diagnose the noise for you.