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?

The manual is available on line at

http://www.hafler.com/techsupport/index.asp?ID=3

Thanks for any help.