This bulletin applies to 2017 Accord L4, and 2017-2018 CR-V and Civic models. A vehicle with relatively low miles may have a hard-to-pinpoint engine knock.
Honda notes that it is currently investigating vehicles for hairline fractures in the crankshaft sprocket, which it suspects is the cause for the knocking noise.
In some cases, you may be able to see these fractures by simply removing the crankshaft pulley. However, the cracks can be very small and you may need to remove the cam chain to ensure a thorough inspection.
If cracks are found, replace the sprocket and the camshaft chain.