Have you contacted Magix? Does this also happen with earlier versions of Sequoia?

Also,  it happens with version 15 of Sequoia as well.  I'm jumping from version 12 (Windows 7) to version 16 (Windows 10).   I did test Sequoia 15 through this process, and same result.

Yes, I understand your point. How would one determine which background task is running when?  My expertise certainly isn't computers...

However, since my original post, the situation has evolved.  The timing of the hash has become much more random and is more frequent as channel count goes up-  the intervals are not predictable. 

It also happens during playback/editing from time to time.  Occasionally, when I initiate playback with spacebar, the audio will be hash.  In Sequoia, toggling the Audio Engine mode one position, then returning to its original position cures the problem for another period of time. 

Magix can't figure it out and asked me to check in with RME to see if you have any ideas.

Yes, it's been very difficult.  I have been working on it with the computer builder and Magix since July.  It was purchased from a very reputable DAW PC company.  I have purchased at least 10 systems from them over the past 12 years or so-  all have been rock solid.  They are completely stumped-  we've gone through lots of BIOS settings and Windows tweaks.

One of those [previous purchases was a 2 card RME System, the exact same as this, except Windows 7 and Sequoia Version 12.  A completely solid system until the motherboard died, necessitating the most recent purchase.  I would hate to think that in 2014 I had no problem with a 2 card system, and computer can't handle that today. That old system recorded many 32 channel 96KHz sessions and concerts, and never once had an issue until the end.

When I run a recording test after some sort of setting change, I usually set the computer to record for several hours, sometimes as many as 12.  The hash usually shows up in the first hour or two, then repeats.  I only ran one 12 hour Reaper test, and no hash.  With Sequoia, the issue has happened every single test (dozens.) 

At this point, I have $5K in this system that isn't working (and two others purchased for an institutional client).  I'll send it anywhere!

These information should have been in your first post already. As the following:

Are these brand new HDSPe AES, revision 2? If so are they on the current firmware version 204? Driver 4.38?

Thanks, Tony.   I should say I only do 32 channels 2-3 times a year.  The rest are usually 8.  This problem is occurring with just one AES input recording. 

High power is active.  Onboard graphics (not Nvidia.)  I could adjust the audio engine slider and run that test, as well as disable network and see what happens.