How to determine if there is a loop in the network?

Question

Computer networks

Good afternoon colleagues! tell me, I understand that this is all strictly individual, but still there is a network in the form of a hierarchy, that is (a router, a core, and further access switches) everywhere except the core there is protection against loops and flooding, but there is one thing, but there are also blunt candles. The question is that recently I noticed that losses began to occur within the network 1 lost packet per 200 sent packet statistically disappears like this, the most important thing is how to use Wireshark or something else to say for sure that I have a loop or storm? Do not judge strictly with Wireshark did not work, so I ask for help in this moment.