This paper presents an experimental testbed to study the noise effect on the performance of the transport layer over Hybrid Fiber Coaxial (HFC) networks. We have successfully designed and implemented an integrated complex testbed, which is suitable not only for laboratory environments but also reusable for real-world networks. The main purpose of the testbed is modeling the residential broadband data network using hardware simulation under several noise conditions and observing the effects on the performance of popular Internet applications as well as native TCP/UDP performances. A large number of public domain Internet measurement tools have been evaluated, from which several selective software tools have been used. In addition, new software has been developed to combine all software and hardware devices. Based on the testbed, we were able to study several issues of TCP/UDP over HFC networks by making a large number of automatic measurements and analysis. The testbed infrastructure would be very useful for cable operator and end users for monitoring and troubleshooting HFC networks, and can be effectively reused for related studies in similar environments such as wireless and DSL.