mechanical noise under the house

My guess is that you have a sump pump. How could you live in a house that long and not know if you had a sump pump? Are you young, first time homeowners?

In my house, that would be the water treatment system backflushing.

It's only been 5 months.... I guess I've just never gone under to look

-- it's a realm with which I'm simply not familiar. So yes; I am a first-time homeowner. Do you think that's a normal thing for a sump pump to do (the noise, I mean)?

Water treatment system?

The gurgling in the toilet doesn't sound right, but the rest of the characteristics sound accurate.

I'm pretty sure I don't have a water treatment system. As for the gurgling, it sounded like it came from the tub (not the toilet).

How about an ejector pump that has a bad check valve....

What's that? For pumping out sewage?

Yup had one in a few houses back, trilevel and was used to send sewage out to street sewer connection!

Pretty sure I don't have one of those, either ... had some plumbing issues a little while back (roots in the pipe out to the street) and it never came up.

I'll have to pay closer attention to things over the next couple of days. Given that I haven't heard it since I opened up the dishwasher today, I'm beginning to wonder if there isn't something wrong there and it just *sounded* like it was coming from under the house. Of course, the rain let up, too; so it could still have been the sump pump. We'll see....

Think water softener.

Oh...OK. I was thinking some other thing. Never mind. :-)

I agree it's a sump pump. Most homeowners spend their first few days in a house learning what the house contains and looking for problems. I suggest you (the OP) do that.

The sump pump may be piped into the sewer, in which case could cause the toilet to gurgle, particularly if the vent in clogged or too small. Many areas do not allow hooking a sump pump to the sewer, but some do, or it could illegally be connected that way.

If it's NOT hooked to the sewer, there has to be a discharge pipe somewhere on the outside of the house. Look for it......

Agreed. Turn off the TV & stereo. Listen to your house. One day, you'll be making bouncy bouncy with the wife and there'll be a weird noise and that'll ruin the whole moment unless you can say "Relax - that was the ".