Battery Draining Battery drains every fews days or so...nothing new has been done to the car, but there now exists a very noisy humm coming through the stereo

Disconnect the stereo and watch the condition of the battery. Most of the time the stereo gets power out of the battery even when engine is off.

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If it is an aftermarket stereo with a subwoofer the person that installed it probably ran the rca cables with the power wire and they should be ran on different sides of the car also a capacitor would fix the battery getting drained

Firstly,you do not state whether the hum occurs when engine is turned off,ignition is turned off or coming through stereo while your idling or in transit. To isolate this problem,you must employ method in your madness.Firstly,with engine and ignition off;Can you hear the hum?If yes,go to the fuse box(normally under the dash) and pull out the fuse/breaker marked RADIO.If hum still there,pull out fuse marked CIGAR/CIGARETTE LIGHTER(after market radio/stereos often attached here) Still no luck,keep pulling fuses until hum goes off.If hum persists, then stereo has been hard wired to the battery directly through the firewall.Re-insert the fuses.
Secondly,If the hum did not occur with engine and ignition off,turn the ignition key to each graduation mark up to the graduation marked IGN( normally this is just prior to the START or last mark.The stereo if wired properly should have come on only when you reached the IGN mark.If hum is present on any previous ignition key marks,it has been wired to the wrong place(fuse box or hard wired)

Thirdly,if no hum present,start the engine.If the hum is now present then hum and battery discharge are not related.(I would look for a trunk/boot/glove box light being permanently on.Next,i would check the EARTH strap connections for being clean and tight( located at Negative battery terminal to Body,Starter Motor to engine and stereo to body( most cheap companies only rely on the stereo touching the body via the stereo bracket.(you can add this wire yourself) Hope this helps.

Do you have a power antenna? It could be the motor is stuck on and draining the battery.