Ok so recently my amp has been making a weird buzz noise. So I thought it was the cable so I changed that and it still buzzed. Then I noticed as I touched my volume and/or tone knob, the buzzing stops. Now I have a Fender P bass where the knobs are metal.

I also tried touching other metal parts on my bass which does seem to reduce or stop the buzzing.

Any suggestions? <3
"Punk is a state of mind, and no one can take that away from you."
Sounds like your amp is not grounded properly. When you touch the metal parts of your bass you are earthing the amp.
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You know you're a bassist when you think a guitar is just some freaky type of short scale, six string bass.

This is The Central Scrutinizer......
It's either the grounding in your amp or bass (and im willing to bet your bass).

Make sure the earth wire is properly soldered to the bridge and that there are no "ground loops".

Im saying its probably the bass because the wiring in an amp will probably be of a higher quality especially with the ground which is after all, a safety device. Bad grounding from a mains powered electrical is a serious fault.

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^ its porbably grounding in your bass. I would take it to a tech and get his opinion.
easy fix, just attach any old wire any old way from the part that when u touch it the buzzing stops, to a metal fixture on the amp or on the ground

oh also try attaching a small wire from 1 of the screws on the jack of the bass, to the bridge (u can just tuck it under the bridge or something)
RG's & Mesa's
If your hands are touching the strings, and your touching of the volume knobs (I assume you mean that you are touching either metal knobs or the a metal part of the pot) then you are affectively completing a ground circuit and that would mean your bridge isn't grounded. There should be a wire under the bridge that it sits on, giving it ground. It could have been pulled through the body if someone messed around with the wiring, or if it's an older bass that's been exposed to the elements, may be tarnished and not getting a good connection. If you have access to a multimeter, test continuity from the bridge to the nut on the jack, which should also be ground.

If your touching a plastic knob on your tone/volume control and it stops then that is another matter and you'd have to look at other things like does your arm cover your pickups when you do this? (blocking feedback) Or is it making the wipers in the pots connect better when you press down on them?

At any rate, use a meter to check continuity of your ground. From your strings all the way to the ground on you amp's AC plug (please unplug first!)

Also, I know my Peavey amp has switches next to the power switch to adjust for ground problems.