The full-scale experiments on acoustic noise recording on the surface of an above-ground pipeline are carried out on operating heating main. The tests were performed in the pipeline branches with different style attachment between pipe and support—rigid (the pipe is welded to the support) and flexible (the freely supported heat-insulated pipe). The experiments show that collection of recorded noise amplitude spectra makes it possible to determine natural frequencies and forms of flexural coincident waves generated by noise in the pipeline spans. Both frequencies and forms of the waves depend on the style of the pipe attachment at the span ends, which may be used in diagnostics of pipeline branches by acoustic noise to detect damaged stiffness of the pipe-support attachment and/or instability of the supports. The computer modeling using the finite element method yields flexural wave frequencies similar to the experiment results. The distributions of nodes and antinodes of flexural coincident waves along pipeline spans at different style pipe-support attachments qualitatively agree with the earlier lab test data.