Originally posted by Lordathestrings
Feedback is caused by the sound of the speaker causing the strings to vibrate.

So when Im standing several metres away from the speakers, with the volume not particularly high, is that just good sustain Im getting? Because I can hold a note for about 15 seconds! I thought feedback was the pickups hearing the amp... ie you can get infinate feedback/sustain even after the string does eventually stop ringing.