Rodent in drain?

I live in arizona. Last night it got cold, and I started hearing scratching noises from my laundry room. I couldn't find anything, and I personally sealed any holes in the laundry room last Feb, so I assume it was something crawling up one of the drains. So i ran the washer and dryer about 10 mins, and I didnt hear any more scratching. I thought the issue was fixed, but just a few hours ago tonight I was using the downstairs bathroom when i heard the same noise coming from a wall the bathroom shares with the laundry room. I assume this bathroom shares the same drain with the laundry room. I ran the faucet and flushed the toilet for 10 mins, and I havent heard the scratching again. Could a rodent be coming up the drain at night when it gets cold out? Is there poison like Drano i would put down the drain to kill it? Last year I had 2 scorpions come up the kitchen sink. In the morning i found them trying to crawl up the stainless steal sink but couldnt. Ive never figured out how to fix the issue. I've thoroughly gone through myhouse and sealed any cracks.