Rarely is there a marginal noisy problem except with grounding problems. If we have a problem with a poor logic bit error rate, then that can be tracked down. As a general rule, BPVs are generated from two sources. One is a poorly performing T1 line repeater or bad copper T1 line pairs. The other source is the last ten feet of line coming into the failing product.
Shiners can easily make an intermittent short to a grounded shelf or anything else.
Thermal intermittents are hard to reproduce without a lab temperature chamber. A can of freeze spray can help once in a while, but this is unusual. Fortunately, thermals are not that common anymore with modern low-power components. Another easy test is to tap an intermittent shelf with the handle of a screwdriver to see if some intermittent component will produce a bit error. If you can get an intermittent problem to the point where you can consistently make it come or go, then you are halfway to solving the problem.