What could cause noticeable vibration less at high speeds in a rear-wheel drive vehicle?

Excessive U-joint angles in a rear-wheel drive vehicle can lead to noticeable vibrations, particularly at certain speeds. The U-joints (universal joints) connect the drive shaft to the transmission and the axle, allowing for flexibility and movement between these components. When the U-joint angles become excessive, it creates an imbalance in the drive shaft, which can cause vibrations.

At higher speeds, these vibrations might manifest differently compared to lower speeds because of factors such as increased rotational speeds and resonance effects. As speed increases, the dynamics of the driveshaft and U-joints can cause the vibrations to either intensify or decrease, depending on the specific conditions and the frequency of the vibrations.

In this context, the other choices do not typically cause such specific behavior at higher speeds. Warped brake rotors generally affect braking performance and would cause vibrations during braking rather than continuous driving. Improper tire balancing usually leads to vibrations that are more pronounced at higher speeds and can affect handling. Worn wheel bearings can create noise and sometimes vibrations, but they tend to be more consistent and not specifically limited to high speeds. Thus, excessive U-joint angles are the most relevant factor for causing noticeable vibration that could vary with speed in a rear-wheel drive vehicle.