Horrible high Pitch Feedback?? Help!

[msandm]

Hi,
This is my first post so I hope this is the right spot.
I use a mackie 8 bus 24 channel desk. I record to computer through an Echo Audiofire 12 interface. I have the direct out from the mackie inserted to the input of the echo audiofire then the output of the audiofire inserted into the tape return of the mackie. When the flip switch is up it is fine to record into but as soon as I press the flip switch down to listen back from the recording I get this horrible high pitched feedback. It goes away if I unplug the lead from the direct out (or the input of the echo) I have tried lots of different leads and it's still there. It's fine to unplug the lead each time when recording one track but when recording 10 mics at once it's quite frustrating to have to unplug and replug the leads into the direct out every time I just want to hear what's been recorded.
I'd appreciate any feedback at all to this frustrating and headaching problem!
Thanks, Damian

 

[mjbphotos]

You've got a loop going there, hence the feedback:

Mackie > Echo > Mackie > Echo

Turn the input off/down on the Echo Audiofire when you listen back. Does the Echo Audiofire have a monitor/headphone output? If so, use that and get rid of the Echo to Mackie tape-in line.

 

[msandm]

Thanks,
No it doesn't have a headphone output. It's got 12 in and 12 out. I do all monitoring through the desk. I can mute the input each time on the Echo which is much less tedious than unplugging the leads each time. The weird thing is that it didn't always do it. When I first got the Echo it did it and I was unplugging the cord every time and then it stopped for a couple of days and now it is again.
Plus it does it when nothing is being played so there is no sound being sent anywhere for a loop to occur unless it just general line noise or something??
Thanks