We are a single family two story (plus basement) home in central Connecticut with city water and sewer. Yes, our home has a proper through-the-roof plumbing vent pipe.

Recently my wife noticed a strange whirring sound coming from the (upstairs) bathtub drain. Honestly, I thought she was nuts, but sure enough now I notice it also. Think of a muffled police siren; whirr-whirr-whirr. Lasts about 5 to 10 seconds, then may or may not happen again within minutes, and so on. Any time of day; a few nights back I woke at around 3:00 AM and, while using the bathroom, there it was. I had not yet run any water, flushed the toilet, etc.

Any hints as to what could cause such an odd sound to emanate from the bathtub drain? It is the only fixture in the house where we have noticed this. I am confidant that it is not related to the hot water heater which is of the indirect-fired type. Our high-effiency gas-fired condensing boiler has a small motorized condensate pump which empties into the main branch (cast-iron) drain pipe in the basement, but I am pretty certain the noise is not coming from that either, though I have not absolutely ruled it out.

Home was built in th 1920's with typical plumbing for that era. Bathroom was remodeled two years ago (and once before in the 1950's perhaps), so bathtub and related plumbing is all relatively new.

 

If the washroom has it's own vent pipe it could very well just be from the wind as it blows across the end of the pipe based on where the vent is on the roof and the direction of the wind during those times. Just a thought.

 

That was my first thought, but the house has only one stack vent that I can see and it is not exactly a direct shot to the upstairs bath.

Also, I am struck by the absolute constancy of the sound. It really does sound like a muted police siren (maybe "rrrr-rrrr-rrrr" is a better description) and always sounds exatly the same in pitch, timing, frequency, whatever.

I am going to have to get someone to help me test the condensate pump to see if it is somehow coming from there - it is the only device in the house I can think of that might be involved - especially at 3:00 AM!

 

We have had a few long threads about mystery noises which turned out to be dying batteries in a forgotten toy.

 

Well, that does raise some interesting possibilities! Certainly good fodder for teasing my wife.

But in all seriousness, that would have to be a very, very, long forgotton toy as our son is 25 years old and a US Army Medic who will be shipping out again soon.

I'll keep it in mind though. Perhaps not a toy, but some other gadget that I hadn't considered. It was the 3:00 AM "visit" that really got me interested because I simply cannot think of anything that might have been going on at that time that would account for the noise.

 

This is a wag, so here goes. With a good vent and a good drain water will drain adequately fast. If there is no ptrap under the tub it will drain excessively fast and could cause the whirring sound. Is there a way to check for the existence of a ptrap? Also how close to the tub is the ptrap? Is there a long leader to the trap itself?
Hey, beats my original thought of a small battery powered disposal unit to take care of hair, etc....
Oh, thank you and your son for his service