Is the amplifier input connected to the "Audio-L" output?
This is probably the DC offset* kicking-in but I don't know anything about the WTV020SD. It may be one of the control signals "switching on" the output. Do you have a multimeter to check the DC output? It should be sitting at half the supply voltage (even when "silent").
It's also possible that there's something wrong with your audio file(s).
I was trying to make a RC low-pass filter between the wtv020sd and amplifier but it's still the same. How can I get rid of this?
If it's the DC offset that won't help. DC is "zero Hz" so it will pass-through a low-pass filter. But you can't hear constant DC. You only hear something when it kicks-in and kicks-out. But, there should be a series capacitor in-between the two to block the DC. If you bought a PAM board/module the capacitor is probably built-in.
* The audio signal needs to switch positive & negative. Since there is no negative power supply, the output should be biased/offset to half the supply so it can swing relatively
negative. Then the bias/offset should be filtered-out with a capacitor. With a single power supply there is almost always a click/pop when power is turned on & off, but there shouldn't be a click when the audio starts.
So i connected the MUTE pins from PAM to the button and when i pushed the button and reset arduino ( still holding the button) and released it after a second the audio was playing without the noise. So i connected the MUTE pin to the 11th digital pin in aruduino. I wrote commends to mute it for first 3 seconds then unmutes but it doesn't work at all. The function doesn't work it doesn't mute the signal. Is it possible that I do something wrong? It worked with the button
Is it possible that I do something wrong?
Yes but unless you post the code and the schematic of how it is all wired up what chance does any non psychic person have of telling you what it is?