Good morning! I'm not the most technical audiophile on the planet, so I am hoping that someone on this board can help me understand a problem that I've been having with my amp. About a month ago, the protect light of my NAD 317 came on, so I took it to my stereo shop to get repaired. When I brought it home, the problem was solved, however a new one arose. When the amp is first turned on, everything is fine, however after about 20 minutes, loud, deep "thuds" start emanating from both speakers. They repeat with a frequency of approximately 7-10 seconds. When I turn the amp off and back on again, everything is fine for a short period, but then the thuds start up again. The time it takes for the thuds to return is directly related to the length of time the amp is shut off...in other words, the longer I let the amp "cool down", the longer it is before the thuds return once I turn the amp back on. I took it back to the store, however they informed me that they weren't able to replicate the issue...so I was hoping that someone out there has either experienced this, or has an idea of what the source of the problem might be. Before I have someone from the stereo shop come out to my house to experience this first hand, I'd like to see if anyone out there has any thoughts/opinions/advice to share. Thanks!