Onkyo says that the receivers that carry the non-safety related defect were made between November 2011 and January 2012.
It's unfortunate, but it happens – products don't always come out flawlessly. Onkyo is dealing with that very problem, and ended up shipping out a good chunk of receivers that are suffering from technical issues. Onkyo wants you to end up with a quality product though, and is offering free repairs to anyone experiencing these issues.
First and foremost, nothing is wrong with the receivers that's dangerous. There won't be fires or sparks or anything like that. Onkyo says that there are two big issues here. The first is that the unit may turn off automatically right as you turn it on. The second is that you may be experiencing noise from the speakers when at low volume.
Hit up the Onkyo Support Page to find out if your receiver is affected based on the serial number. We've included the full list of receivers below.