I have built an audio amplifier using TDA2030. The amplifier works fine with very low noise, the input is given through 3.5mm jack of my phone. Everything works fine until I touch or pick up my metal phone, as I touch my phone the speaker starts giving out a loud noise until I place it back on the table.
Note: C1= 20uF in my circuit
Edit: It's a continuous buzz sound. It is the same type of noise we get when we touch an unplugged 3.5mm jack. I am providing power through a 12V 2Amp rated adapter (which is giving 18V output when not connected to load). I am using long wires to build the circuit. Actually, I used a breadboard to build the circuit and test it.
Many of you are suggesting that it's because of improper grounding. Please explain this because I am not getting your point, I will be happy to learn a new concept. And suggest a method to fix the noise.