ttworld wrote:

: Recently only one channel my preamp started having random crackle and
: pop noises. The music on this channel also sounds distorted when the
: crackle and pop noises are present. The noise is only intermittent.

: The noise is not affected by the signel source, dub and mono switches,
: the balance and volume knobs nor the tone switch/settings.

: The functional block diagram on page 21 of the Hafler manual shows only
: the high level gain stage and the dc feedback sections as unaffected by
: all of these controls.

: Can anyone suggest where to look / test for the source of these
: noises?

Have you tried posting your question on:

www.dyiaudio.com

Its a forum that has a lot of knowledgeable people that could help with
your problem.