Could it be the sweet smell of formic acid that’s produced by ants?

Since you say this started after heavy rains, perhaps get your house checked for leaks and mold growth. While some molds can smell earthy, musty, or rotten some of them are noted to smell sweet.

I hadn't considered an ant issue, that's interesting. There's been no visible ant problem, but I think you're saying maybe there's a nest or something and they're creating that smell.

On the mold idea, I didn't know that mold could smell sweet. It is very odd that I smell it at a few other houses on the block when I'm walking on the sidewalk, which made me think it was somehow groundwater related, but who knows. I know that mold testing can be unreliable, but it's just odd that it's this whole new smell. It's really getting to me.

If it’s ants, that would explain the smell after rain - rain makes the ants active here. It would also explain why you smell it near neighboring houses, by the sidewalk, etc.

If it is ants in the crawlspace that are making the smell, I am wondering what the best nontoxic way to get rid of the ants/smell? I've rarely seen an ant inside, so it's odd. Wow, I had no idea ants could smell so strong.

If it is ants, there are a few different homemade recipes using borax that should work. Do a search — I have successfully used the one made with borax powder, peanut butter, and honey.

My friend had this exact smell in an older home they purchased, pulled up all the floor boards/carpet and it was determined to be old pet urine.

Does your heater use gas? If so please call your HVAC tomorrow and ask him to check it for you. I think you have either a Freon leak or gas leak. Freon usually causes a sweet smell when it leaks. Let him check if you have an AC coolant leak. Also gas leak from a broken heat exchanger can causes an intense surge smell that masks the rotten egg smell of gas.

Thanks, KR. Did your friend smell the odor in their crawlspace as well? I'm curious how/if they got rid of the smell. I'm also curious how they knew it was old pet urine. Sounds like it's the same strong sweet smell, maple syrup and often pungent. We have hardwood floors and I've cleaned them many times. I had thought that maybe it was old rodent urine in the crawlspace and the smell is coming up.

Thanks, Lila. It's definitely not a gas smell and we don't have an AC. We actually don't use the heater at all. Would it still be possible to have the smell from a broken heat exchanger even though we don't use the heater?

A furnace left out of use can sometimes acquire condensation. This condensation then accumulates in the heat exchanger, which can cause it to rust and consequently crack.
Do you have a carbon monoxide detector in your house?