I've been slap-popping a lot lately, and I'm having trouble on my Ibanez Ergodyne 605B. The only string that slaps well at all is the B. Whenever I try to slap on E or A, I get this weird harmonic-sounding ringing. The D and G pop perfectly, and all the strings sound fine when I play fingerstyle. Is there anyone else who's had a similar problem? Any easy fix, or do I need to adjust my technique? Anyone?