Wierd right hand problem

[TenaciousE]

Let me run something by you guys. I play fingerstyle, and I lightly rest the side of my thumb of my right hand against the strings but don't really anchor my thumb. After I pluck a string with my index or middle finger, the finger hits the next lower string and then comes to a stop. I've been playing for a number of years now and never had a problem with this technique before. It feels very natural to me.

Well, the problem is that I got a new bass last week, which I love. But, I've noticed that when plucking the A or D string(it's a four string bass) with my middle finger, my middle finger is making a "thunk" kind of sound when it hits the next lower string (A or E). My index finger doesn't seem to be making this noise. It's most noticable when plucking the open strings or when fretting one of the first five frets. I don't hear it when I'm fretting higer up. I hear it whether the bass is plugged in or note. I just played my other two basses, and I can't hear any noises with plucking these basses.

I guess it might just be poor technique since I notice it with one finger but not the other or maybe I just need to make myself use a lighter touch when using this bass (I don't pluck that heavily now), but I wanted to see if anybody had any thoughts.

Thanks!