The first thing I always say when an audio device is giving a low frequency hum: “Bad caps!”. The NAD L70 DVD-receiver was no exception in this. 🙂
Bad and bulgy electrolytic capacitors.
After testing the hum was gone, but unfortunately the CD/DVD player was not in a very good condition. What it needed was a new laser unit.
I ordered one from aliexpress and after quite a while (because of a mistake of the local postal office in The Netherlands who did not notify me of the package and returned it after three weeks) I finally got a new laser unit and the NAD L70 was as good as new again!