I have an NAD C352 here that's about 2 years old. Just recently, the right channel got very quiet while I was listening to music. I powered down the amp, then powered up again, and when I did, I got about 3-5 seconds of quiet static hiss in the right channel which quickly died off. Then, when I started playing music again, it was very quiet in the right channel.
If I leave the amp off for a long time (say, long enough to let any caps discharge), then it sounds ok for a few minutes on power up, but then the right channel goes again, and I can hear it fade away over a few seconds, around the same time that the hiss mentioned above would last.
The pre-outs do not have this problem - I'm running stereo subs off the pre-outs, and they sound fine, so I'm taking this to mean the preamp is ok and this problem is in the power stage. All cabling has been checked, two different sources tried, speakers swapped to make sure they were alright. It's definitely just the speaker-level outputs of the amp displaying this problem.
I Have nadc372(150watts per channelx8ohms) and i guess urs is more or less the same... Check with service center, and I have mine for over 5yrs and keeps sounding better day by day... no problem encountered as such......
Most likely one of the output capacitors has failed. I suggest you do not use the amp until you have it repaired. If it is an output capacitor, there is a low risk chance that the component can fail violently. In this situation, the contents could spread themselves over the motherboard and render the amp un-repairable.