Echo through Hats grouping

I have just watched tutorial 11 and it goes on to say group the Hats, now when I do that I get a severe echo through my ear phones from ableton and the tutorial video, but when I removed or mute the Hats group, its disappears, any ideas?

when I click on the hats group and take out ext in and move it to no input, echo disappears, but on the tut video yours is set to ext in, dunno if this will affect it?

You are exactly right to change your ext in. You are experiencing feedback. This can happen with built in mics etc.

Perfect cheers phil