I heard the hard disc spin up regularly as it wrote data out.
0.75 seconds worth of 4 channels at 16/44.1 is about 256 kbytes.
256 kbytes is a nice round number and would make sense.
But I thought you recorded at 16/48?
(All assuming we left that 4th channel running, which I think we did)
edited to add:
ok so i looked at the user manual for the vf160, seems it only does 16/44.1, so that's probably it. it's unlikely to be the mics picking up the noise, rather it'd be more likely to be the internal electronics being upset by the relatively large current being drawn as the hdd spins up.
now, i don't hear any noise on my m10, which was hanging off the back of the fostex, but in fairness i've not been in a position to crank the level to a point where i could hear it (and neither have i been in an ideal listening environment). i wil get these files to you asap (but obviously they're already mixed down to stereo)
edited again to add:
fwiw back in the jb3 days, i recall some people complaining that their jb3's picked up hard disc noise. i was fortunate in that i had to add crazy amount of gain to make that noticable on my jb3. luck of the draw i guess.