First, leave the preamp turned off and just power/listen to the power amp. Does it make any noises after a half hour or more? Does it make noises on power on or power off? If so, it should be repaired. I've had 3 DNA-1s and none them make any such noises.
Second, if the amp behaves well, then it's the preamp.
BTW, are you confident of the connections in your DIY ICs?
Second, if the amp behaves well, then it's the preamp.
BTW, are you confident of the connections in your DIY ICs?