Could it have to do with the slightly denser air at the cooler winter temperatures? Since sound doesn't travel in a vacuum, going towards the other extreme could mean better transmission of sound. Seasonal humidity differences might also make a difference.
Or maybe your earwax is softer in summer. Or maybe your outer eardrum cells are drier and less pliable in winter. Or maybe the coclear fluid in your inner ear is slightly more viscous with the cooler temperatures. Or maybe when it's hot you have different bloodflow patterns in your ears. Maybe snow and ice act as ambiant sound absorbers or diffusers.
My best guess is that it's just generally quieter and your equipment likes the temperature better.
Or maybe your earwax is softer in summer. Or maybe your outer eardrum cells are drier and less pliable in winter. Or maybe the coclear fluid in your inner ear is slightly more viscous with the cooler temperatures. Or maybe when it's hot you have different bloodflow patterns in your ears. Maybe snow and ice act as ambiant sound absorbers or diffusers.
My best guess is that it's just generally quieter and your equipment likes the temperature better.