Reply to Help with turntable buzz...tonearm or cartridge problem?

Hi guys, hoping someone can resolve this problem for me!

I have two second hand Gemini TT02 turntables, I want to use Traktor scratch with them but even when I try to use normal vinyl I just hear the typical problem 'buzz' sound. So i know there's a bad connection somewhere but hoping someone can help me workout where!

Here's some more info - The mixer is new so its not that, the ground cables on the turntable and the mixer and attached securely. The buzz still happens when the turntables are off.

When playing the vinyl at first I couldnt hear any music, like the decks weren't amplifying the sound due to a bad connection, but when I licked the back of the concorde cartridges (I know this is bad but it was just to test!) and attached them again, the sound came back perfect on the right deck, and ok on the left but still with a faint buzz.
Also when i tap the tonearm, a sound comes out of the speakers like when someone taps a microphone which i thought was interesting, any suggestions as to what the problem is, or whether its the tonearm connectors, or the cartidges themselves? I really want to get this fixed but don't have money to be buying everything to try it out!

Thanks!