a good thing to say when people say bass is easy.... bass is easy to play, but hard to get good at. and the thing i hate the most is playing with a ****** drummer
if you have a 9volt in the back of your bass and it is starting to lose its juice it makes the exact sound you are describing. just check to see if you have one in your electronics compartment
a hartke combo amp is great for small bars. they pack alot of punch and are not that expensive versus sacrificing getting a cheap half stack just for the sake of having a half stack