What kind of foam rubber? The round kind that is black? It'd have to be like half inch diameter or so right?
I notice on my P-Bass type Yamaha RBX I get some funny sounds when I fret the low E string anywhere below the 5th fret (A). Anything above that point fretted sounds ok...but I guess this is what you guys are talking about on a bass? (overtones) When I play octaves on the E and D fretted below the 5th fret the weirdness goes away...I'm assuming because I've introduced a more solid vibrating note on the D so the ear automatically hears that better. Its not that bad, but I think I am hearing overtones like the kind you are talking about. The bass IS intonated btw.
Oh also...won't the foam make the strings vibrate less?
Guitars/Bass - MIM Fender Classic 50s Strat, MIM Fender Standard Strat, Squier Classic Vibe 50s Tele, Gibson Les Paul Studio, Epi '56 Gold Top Les Paul, Martin DSR acoustic, Sigma Martin Auditorium electric/acoustic, Squier Jazz Bass.
Amps/Cabinets/Modelers - Model 2558 50 watt Marshall Silver Anniversary Jubilee combo w/ Celestion Vintage 30s, 4x12 Marshall cabinet w/25 watt Greenback Celestions, Fender Blues Junior w/ a couple of Billm mods, Line 6 POD 2.0, Roland Micro Cube
Pedals/Effects - Cry Baby Classic Wah, Boss TU-2, Boss NS-2, Boss RC-2 Loop Station, Ross Compressor, MXR Micro Amp, Danelectro FAB Echo, Danelectro FAB Chorus, Danelectro Chicken Salad, Marshall Guv'nor Plus, Marshall Echohead, Duhvoodooman's Zonkin' Yellow Screamer, Digitech Digiverb, Digitech Bad Monkey, Dunlop Fuzz Face, Homemade Loop Bypass pedal, Duhvoodooman's Sonic Tonic (Maxon SD-9 clone +), Voodoo Labs Superfuzz