Whilst my area is really inductor based power supplies, I thought you may be interested in the article here: http://www.tnt-audio.com/clinica/regulators2_impedance1_e.html This looks at the impedance of the LM317 across frequency and the anecdote at the end may be a similar problem to the one you are having - the LM317 may be oscillating due to the low esr input cap on the ADM660.
There are a few things you could try to help
- Add a capacitor into the LM317 feedback loop to improve the low frequency performance
- Ensure there is a continuous load (the output impedance of this type of regulator tends to improve under load)
- Add a ferrite bead between the LM317 and the input cap of the ADM660 - it may help reduce high frequency noise
You may also want to try changing the ADM660 switching frequency - I believe you can either set 25kHz or 120kHz. One frequency may give better performance for you
