Abnormal Noise, Heat, Vibration or high Wear metals
Any abnormal noise, heat or vibration should instigate sending an oil sample to establish the cause of the problem (unless another NDT technique suggests immediate stopping of the machine to prevent catastrophic failure). If the analysis result is time critical it may be worth contacting the lab to discuss your options for urgent analysis.
Whether the oil report or another investigation suggests a high wear process it is worth establishing the cause in a methodical manner. On smaller systems the cause may be quite easy to spot as there are only a limited number of components involved, but a wear debris analysis can aid in identifying potential contaminants and wear modes to narrow this down further.
On larger systems there can be multiple points of failure, and so this is where if taking from one primary sampling point it may be worth taking from additional secondary sampling points close to components but before any filters. These samples will reveal the highest concentration of wear metals and hence the likely source of the wear and failing component.
Likewise, if the system has filtration, then much of the wear in the system is likely to get trapped in the filter, rather than remain in circulation, hence submitting the filter for analysis is an excellent way to detect the root cause of a problem. Filters concentrate the wear metals and contamination in one place, helping to assist the root cause analysis procedures.
Note: It is never advised to make a costly shutdown or component replacement on the back of one single oil analysis report. It is best practice to build a trend and ideally use confirmation tests to confirm oil analysis findings (such as abnormal noise, heat, oil volumes, top-ups, pressures, filter replacements etc)