So I picked up my Sportsman 2 years ago used with the original Carlisle tires on it. Over the summer the front right tire started losing air slowly while sitting in the garage. About one psi every 1-2 weeks. Prior to this there was no problem. Yes, the tires are in good shape and there are no nails or screws in it. Should I take it off the rim and check the inside of the tire?

I am very confused as I mostly drive mine during the winter for plowing and ice fishing and this started during the summer months,while it just sits. Thanks.