Ver slight background buzz after switch on (but not noticed during playback).
I recently obtained the Rio600+32MB backpack at an absolute steal of a price (£25, ~$37) on sale at the 'Scottish Power' closing down sale. The Rio itself came with version 1.07 firmware. I plugged the Rio into my iMac via the USB lead and it was immediately recognised by iTunes in Mac OS 9.2.1 or Mac OS X 10.0.4 as an external device without any software installation. I connected the backpack and upgraded the firmware to version 1.15. The Rio600 showed up as a single device with 64MB memory (seen as one 64MB internal and 0MB external memory) but the installed demo tunes were wiped (not a great loss). After looking on the excellent Rio help and support pages I noticed that there was a firmware update (version 1.56) to allow support of 128MB backpacks - I downloaded this and updated. The single 64MB device was split into two 32MB partitions (one 32MB internal and one 32MB external memory) that have to be filled separately. Before the update I could just make up a 64MB playlist and copy it over - now I have to make up two 32MB playlists losing space at the end of each list. If you have or are going to get the Rio600+32MB backpack DO NOT UPGRADE FIRMWARE TO V1.56, USE V1.15 as it is not possible to downgrade the firmware. The support offered on the Rio site in the form of drivers, software and firmware updates is execellent but this problem (or possible rectification of an otherwise useful inadvertent feature) was not covered in the firmware Read Me files. Other than this slight gripe the player has been excellent to use and I'd highly recommend it to Mac OS users.