Every time after I take a shower, I can hear the sound of "bank" from the drain pipe under the bathtub for almost two hours in every 5 to 10 minutes interval. Any idea why does this happened and how do I fix it? The house is about 1 year old.

Could you explain "bank" a bit more or in different words? Of do you mean bang? Bang is not a drain sound complaint I have heard so far but you could be my first. Bob

Describe the noise you hear a little better then just "bank".
Give us something to work with. Cheers, Tom