Whenever we perform a transfer on Polygon we get some other transaction from another address different from the receiver that is sending us back a pretty small amount. Any idea what this might be happening?

Someone is trying for the dust attack. In such an attack, the attacker or scammers sends a very tiny amount of funds to a large number of users' personal wallet addresses, it's less than the transaction fees required to spend it and it's known as dust. They then track these funds and all transactions of the dusted wallets and perform a combined analysis of several addresses, enabling them to link the addresses. Eventually, they then determine the identity of the person or company behind an existing wallet.

If they succeed in determining the identity, then the attackers may use this information against the wallet address owner either through planned phishing attacks

here is the complete article for the dust attack and how we can avoid that: https://www.gemini.com/cryptopedia/crypto-dusting-attack-bitcoin