Area where driveshaft goes into differential makes chirping noise after driving.

What is your question?

After a fifteen to twenty minute drive there is a chirping noise coming from under my car. It is relative to speed, when I slow down the noise does and when I speed up the noise follows. It is not really noticeable when driving over 40mph. On one occasion the noise went away and came back. If I hop on the highway, then get off the noise is always present. Any ideas would be greatly appreciated. It IS SOOO ANNOYING.