After my bathtub is drained it starts making laser gun sounds "peeerrro" (I don't know how to spell it). It will make the sound and as soon as it stops begin again, then again, on and on until they get longer and eventually stop. Over the last week it has been getting louder. I don't know if it matters but we have a septic tank not city sewer. Any guesses as to what it might be?

This sound starts when you open the drain and continues until the tub drains? Does the sound come from the tub waste as it's draining? Any gurgles?
This "laser gun sounds "peeerrro", is it like a high pitched squeal? Any other noises from the other fixtures? Let me know, Tom

The sound in the bathtub starts after all of the water is gone so there aren't any bubbles or gurgles from the water. The sound isn't a high pitch, it almost sounds like someone strumming a loosely coiled spring. It is the weirdest thing. I could take an audio clip and send it if that would help. When our washing machine drains it makes a "glug glug" sound and then the sink "glug glugs" immediately after. I don't know if the washer/sink are connected to the sounds we are getting from the tub.

When our washing machine drains it makes a "glug glug" sound and then the sink "glug glugs" immediately after. Well the "glug-glug" indicates that you're pulling air and venting through the traps. You could try this. Rent a sewer machine and snake all your roof vents. On all the vents put out enoughsnake to reach the base and 16 feet more. Let me know if it helps. Tom