Dripping heard when draining tub

I have a problem. When I run a shower or when I drain the tub on the top floor, I hear dripping on the floor below. If i put the plug in first, and then run the water, I hear no dripping. This leads me to believe that the problem is not with the water supply but with the drain. Forgive me if I'm using newbie terms, I really don't know what I'm doing. A colleague of mine, who just moved into a new house has the same issue, and he feels that it is just water dripping within the trap. As info, my house is about 7 yrs old but I've only been in for 2 months, and the dripping has happened the whole time I've been there.
Any ideas? Thanks very much in advance.
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bigredmoose wrote:

A 7 yr old house no doubt has plastic (PVC/ABS) drain piping.
Very often, "dripping" noises can be heard from water falling *inside* the pipe (not leaking out) because plastic piping transmits noises so well, rather than absorbing them.
If you don't see signs of wetness anywhere, chances are this is what's happening.
Jim
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wrote:

Just some thoughts. I moved in to this house 22 years ago, when my house was 4 years old, and some of them were 5. In the next two years I visited about 6 houses, 2 of which had already had repairs to the dining room ceiling because of leaking from the bathtub. I"m sure they repaired the drains when they repaired the ceilings. And I think I was told about one or two more, and it's not like anyone knew about all 100 houses. I have plastic drain pipe everywhere I can see it, (which I guess is every place but the tub and the shower.) and the neighbors have the same.
Periodically I would find water in the glass ball that surrounded the lightbulb at the bottom of a chain (in my ceiling light fixture.) I emptied it, or it evaporated, and I guess it never got deep enough to break the light bulb. It's really interesting, since the fixture is at least three feet from the drain upstairs, and there has never been the slightest stain on my ceiling.
Until recently, the last time it leaked was 15 years agog when my brother took a long shower. I otoh use it almost every day to take a bath, and no more leaking. I'm guessing that when I drain the tub, there is more water going out and more siphoning suction that lessens the leaking.
I'm also thinking, since it used to leak even when I used it, that the hole has been plugged by the crud that comes off my body when I bathe, mostly dead skin.
For some reason, I found water in the glass globe again recently, a half inch or so, but only once. I think some of the crud got washed away by draining water, and then got replaced after my next dirty bath. After all, the water leaking out would be carrying its own stop-leak with it.
I live alone and don't have guests in the last few years, but if they wanted to shower, I might have them use the shower off my bedroom, where there has never been any leaking (in my house or the others afaik) But that might not be necessary now.
If I were you, I absolutely wouldn't do anything until the ceiling below got stained. It might be dripping within the pipe, or it might be leaking, but I've gone 22 years with no problem and no water in the globe from probably 14 or 18 years of those 22. Repairing it will be from the bottom anyhow, so you might as well wait to see if it ever leaks.
I'm 70 pounds overweight now, 220, and the bathtub makes a snapping noise on the right front, next to the wall, once each time I get in. But it hasn't sagged with respect to the wall tile, except maybe an eigth inch at hte front left corner. I've been watching that for years and it hasn't increased. So I don't think the wood underneath is being damaged.
Remove NOPSAM to email me. Please let me know if you have posted also.
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@bigfoot.com says...

Assuming, of course, that 20+ years of leakage hasn't caused rot.
--
snipped-for-privacy@phred.org is Joshua Putnam
<http://www.phred.org/~josh/
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Try to localize where you are hearing the sound come from. This happened to me last year and I discovered a leak from the tub drain trap which was dripping across a tub support stud, and dripping onto a bottom plate behind a return vent on the floor below. I had my wife and kids stand around the perimeter of the room with everything except lights turned off to hear where it was coming from.
Jon

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