HELP! hammer on playing two notes at once

[fodera of doom]

I need help. I am having problems with my bass playing two notes at once when I'm playing hammer ons. I'm only hiting one string at a time but it sill dose it. Is it a trust rod problem or something?

[Kronos]

Are you muting the other strings?

[brane]

If you are hammering on to an open string, you will set both halves of the string vibrating... so you are hearing the part between your finger and the bridge producing a note, and the part between your finger and the nut producing a note. Luckily, the pickup will only, um, pick up the part of the string vibrating over top of it, so it's only a problem while playing unplugged.

If this isn't the case... then I have no idea, other than, yeah... make sure you are muting the rest of the strings so you aren't setting them in motion through sympathetic vibration, as Kronos suggested.

EDIT: Just occured to me that it doesn't have to be an open string... but that's usually where it happens because most people don't stretch their hands enough to hammer on a note that far away. Though, it also shows up when tapping too, for the same reason.

[nowontonsforme]

the pickups will definitely pick up some of the other note if both halves of the string are vibrating. on one of my basses this doesnt happen, and on the other its a big problem. to stop both halves of the strings from vibrating you can use a scrunchie to mute the top half of the strings. the problem with this is that it mutes all open strings as well.

[fodera of doom]

the scrunchie did it.
thanks!