Yes trouble with ND 3500 though was that it always read CD and DVD's att full speed making a terrible noise.
This was no matter of what was read, CD, DVD, CD audio - it would spin up max even if the disk was touched in Explorer - and keep on spinning..
Felt to me like som bad piece but tried several versions, several Nec players on several motherboards and always the same problem..
ND-2500 was much nicer, only spinning up when it actually needed and spinning down quite fast if it found it didn't need too.
(for example playing dvd or cd audio)
So that kept me wondering if the ND-3520 had this problem fixed.