My rumble 30 bass amp makes a lot of bad noise when i plug it in. it started off when i first started playing it and it worked fine, then after a few minutes it started making the noise. i've tried two different basses (an accoustic/electric and an electric). i've tried different cables and different outlets, nothing seems to work, im convinced its the amp. now everytime i plug it in and turn the power on it starts that noise

A silly suggestion is to plug in a different guitar and see if the problem still happens. Have you checked the link your using to connect to the amp? For example is it a faulty lead, a loose jack plug on the end of the lead or an intermittent signal from a wireless connection? You could also check the pickups on the actual bass guitar.
Pick ups don't often cause issues but they can become faulty because of age, corrosion, short circuits and if they're badly fitted.

Your amp has two inputs - Passive and Active. Do you get the same results plugging into either one? If only one works, then the other needs reconnection or replacement.

The small Fender products often have a TDA2050 power chip in them. The chip is on a thin aluminum heatsink and is intended for light use. If you try to sound like a bass guitar amp with this, the chip will go into thermal protection mode. Cutting vents will not help very much, and pushing it to these levels will destroy the speaker eventually. If you need more power, buy a bigger amp. This one would be suitable for a 10 foot by 10 foot room.

Try plugging another sound source into the unit. The buzz MAY be pickup of magnetic fields in your guitar pickup that clobber your notes from the strings. Bad guitar cables are another possibility. By putting clean music from say a CD player into the unit you can find where the source is. If the CD player generates the same noises, then likely you have a failure of filter caps in the amp or other component failures. Also make sure your guitar can't "hear" the amp as feedback can do strange things.

First check speaker and speaker wire.

There is an inconsistency in your text. You indicate that cables were swapped and problem still existed...
You said:... "i have tried using it on a different amp and still fine".

If you tried it on a different amp and it was still fine then the guitar is probably OK.

THEN your amplifier is in question as the root of your problem.

What is the amp you have? The guitar is the CB-42, but what amp do you have?

MANY intermittent problems with amplifiers are often with the input jack itself. These jacks are easily broken by tripping over a cable plugged into them.

It unfortunately sounds like a blown speaker. Try getting at the speaker and gently moving the cone with your fingers. If you feel a rubbing sensation you will most likely have to consider a new speaker. Make sure you get one with the same impedance (ohms) and the same or better power handling.

caps

I just fixed my bass amp with a similar problem last week: the problem is related to a loose connection on the PCB board (likely).
A bass amp is a rough place for circuitry: the low rumble and power shake a bass amp more than a guitar amp.
In my case, the power transistors needed to be re-soldered and then the grounding bolts and screws needed to be removed and cleaned because the connection was bad. Remember that when two different metals needed for an electric connection are toughing, there is the likelyhood that corrosion WILL happen.
My bass amp did basically the same thing yours did: sounded good at low volumes, but at higher volumes it would act up.
In short, there is nothing you can do (unless you are a repair person): you need to take it to a local music shop and have a tech fix the intermittant contact problem: someone who knows what they are doing should only take an hour at most.

Hope that helps!
-mike

Replace C21 (10uF/50V) and C38 (2.2uF/50V) and it will work great.