Bizarre issue (Audio Alchemy)

Well...my first post here is unfortunately a "cry" for help. 
I recently purchased an Audio Alchemy DDP-1 DAC/pre amp. I paired it with the PS-5 power supply upgrade.
I am using a Classe' CDP10 player with option to run the transport to the Alchemy DAC or the Classe' DAC to the Alchemy analogue stage.
The rest of my system is a Rega RP6 with an Audio Alchemy phono stage and a Krell KST 100 into Revel M-20 Performa speakers. Interconnects are all Blue Heaven II's save for a PBJ phono to DDP-1 and a Moon Black Dragon digital connect from Classe' out to the Alchemy digital in.
Everything is plugged into a PS Audio Dectet.
I am gradually upgrading everything.

Here's the problem.
The rig runs exceptionally well-- no complaints re: the sound--until after a few hours there is a 'sudden" loud fog horn sound from the speakers. I mean LOUD! Literally blasting. I can find no reference on line to a similar sound. This sound is not impacted by the Alchemy volume control and can be eliminated only by shutting the system down. It does not return upon re-start until an hour or so later.
I suspected the Krell. I replaced the Krell with a pair of powered Audio Engine 2's and after a while same problem returns.
I removed the phone pre-amp using digital source only--and problem remained
I then suspected the power supply for the Audio Alchemy and returned it to the retailer --it was replaced and sure enough after several hours of perfect running the fog horn returned!
I am now planning to contact the retailer and have the DDP-1 replaced. I also will e-mail Peter Madnick at Audio Alchemy.

Thanks to anyone hanging in to this point. I am wondering what the knowledgeable folks out here think.
Any thoughts and advice would be greatly appreciated. 

I have to say--the Audio Alchemy units are terrific. Great sound (especially at the price point). I am somewhat certain the issue is somewhere with one of the three AA units--process of elimination has me down to the DDP-1.