search warrant issuance and procedures in MN state, grounds for police entering house without a search warrant

Here are just three viable examples of what might cause police to come in to a house to search.

... smelling an odor of an illegal substance being smoked inside.
... hearing loud noises that suggest disorderly conduct is going on inside.
... hearing a scream for help by someone inside.
.. seeing a view that some crime like battery or use of a weapon is going on inside

Police can use their senses of sight, hearing and smell to come into a house to search.

I hope this helps.