My bath tub is making a knocking sound. how to fix it?

there is no water on and u can hear a knocking sound coming from the drain. its not all the time, but it does it for like 5 mins then goes away or a few hours then comes back. and it doesn't have a rhythm.My bath tub is making a knocking sound. how to fix it?
sounds like the drain pipe has come loose from whatever wall bracket was holding it.... if you have easy access to the drain (ie. in a crawlspace or basement.) check it out... find the source of the knock.. use metal or cloth strapping tape to resecure it...





if your not so much a do-it-yourselfer.. you may want to call a plumber....

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