The script to reboot on no-sound is here:
http://www.tivocommunity.com/tivo-vb/sh ... &page=2#35or by "install nosound" if you have my install script on your tivo.
A new PSU doesn't always solve it - certain brands of HDDs also make it worse (hitachi) as well as cachecards/ram.
You can increase the 5v line slightly by turning the blue pot on the PSU anticlockwise a quarter turn (when turned off!).
At present many working tivos are being given away or sold for next to nothing on ebay and elsewhere, so keep an eye out !