Very few people with chain drives have any predictive or even non-intrusive inspection programmes for chains. This is a shame since it is so easy to inspect a chain using ultrasound. As a chain link moves over a sprocket two things happen. Firstly, the chain link bends and secondly a tooth of the sprocket must slip though the link and make contact with the pin. This is all going to introduce friction and therefore ultrasound which will show impulses corresponding to each of these movements, with a degree of periodicity as the chain repeats its circuits:
Tip provided by Tom Murphy and Allan Rienstra, Authors of Hear More A Guide to Using Ultrasound for Leak Detection and Condition Monitoring.