Well a moron "friend" of mine dropped my bass and ever since it gives me some weird feedback. Sometimes is like a hissing sound (the amp already has some of a hiss, but the bass makes it way louder and it's with this bass). Sometimes the amp will do a weird high pitch sound that only this bass does since it was dropped. I've noticed the sound goes away a bit when i turn the treble down. Do you have any idea what it could be, and how I can fix this?
A friend of mine said something about the treble knob, but I can't remember what exactly.

Any help is appreciated. Thanks.
i recommend finding a good luthier and having them take a look at it. it might be something simple, but it's better to get someone who knows what they're doing to fix it. your local guitar/music store can probably recommend someone, or they might have a luthier in-house.

just courious...what kind of bass? is it active or passive? when he dropped it, what took the brunt of the force? is there any obvious signs of damage from the drop?
Sounds like you cracked or broke something. Maybe a pot, capacitor, intermittent wire connection, solder joint, ground. etc. Have a pro look at it or do it yourself using a voltmeter checking for continuity and resisitance. As a musician you should know how your intrument is wired, or Google your model for electronic schematic.
The part that wouldve taken the damage would be the headstock, so I don't really understand that. It was rasting vertically against my amp and it was inside its bag, so the fall wasn't that big, I assume...
I'd sa its a round issue. Check all the solder joints and if they are stable check where the ground connects to the bridge......if its not active pups that is.