*One year later* - Resurrection time.
Yeah; I`m guessing that my computer has a pretty crappy sound card, very consumer level. It does its job as a decent way for me to record LPs, and play back music. That 7khz spike is almost undoubtably all from the computer.
That being said, an audible high-pitched hiss can be heard from both the Z5 and the ZHD... I might end up using my school's "Logger Pro" sound analyzer softer+hardware to check this. But the unlikelihood of that is very high...
Has anybody else more thoroughly tested the ZHD's SNR yet?