Why is my plumbing or AC making bubbling noises?

What people tried

Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.

1. 1
   Calling an HVAC or plumbing company for assistance
2. 2
   Using a shop vacuum on the end of the condensate drain pipe to clear clogs
3. 3
   Shutting off the water supply and draining the system to rule out plumbing leaks
4. 4
   Checking the furnace cabinet, coil, and drain pan for moisture
5. 5
   Inspecting suction lines and duct dampers for loose parts
6. 6
   turning on the water faucet to stop the noise
7. 7
   waiting to see if the issue goes away on its own

In their words

Unedited, most upvoted first, each linked to the thread it came from.