Damn Neon Lights!!

Yes, there are true line conditioners out there but they are expensive. I can't think of any brand names at the moment but I know a few guys here have talked about them before.

BTW, does your amp have a ground lift and if so, did you try it?

 

I thought that this post was going to be about not liking that Kraftwerk song

 

Furman power conditioners, have EMI/RF filtering standard, even on their cheapest models, that will filter that crap out.

 

Try this: next time you play at one of those joints, turn your amp on and up a bit with no input plugged in. If you're getting hash noise from the neon through the AC, a good power conditioner may help. If, on the other hand, you only get the noise when your bass is plugged in (quite likely, this), the problem is coming from your pickups picking up EMI and a power conditioner probably won't help a whit. It's possible for your amp to pick up EMI directly from the neon rather than through the AC line too. Shielding is your friend in that case, and sometimes it's your friend if the bass is picking up EMI as well. A lot of times it won't fully solve the problem though.