it’s a known issue, multiple threads on it unfortunately… my feeling is that is just a not very powerful headphone amp put in to this units compared to others… (some low impedance headphone seem to have it quite bad compared to others that have better results such as bayer)
this problem was prominent on any type of HP solution with low impedance i was using.
i’ve went a great deal of back and forth with support and tried a few different quad’s and the problem persists in all of them…
workarounds for me were:
-cheap desktop stereo headphone amp (problem solved)
-seems to be less prominent when i have xlr out 1 & 2 connected to my studio monitors
-higher impedance headphones ( a lot of people don’t seem to have this problem with them)
-for my case having a high MULTI OUT level(0db) and a Low HP Level (-24db) seemed to be the magic ratio to have it without doing it the annoying clipping on the spikes
I will post below their email response to both the dealer and me about this issue.