We have gas steam-heat radiators in our 1936 massachusetts house, which we moved into last fall. In the living room they are decorative built-in radiators, flush with the wall with a space behind them. It's very difficult to get into that space. Just recently I have noticed a kind of sweet musty smell coming from them. It's hard to describe: not just an ordinary musty/dust/mold smell, but a distinctively sweet dusty/musty smell. I hate it! I didn't notice it in the winter when the radiators were actually on. It seems like it wafts in on a draft sometimes--like the radiator has bad breath. I *did* smell the exact same smell in a closet of our old apartment from the same approximate era. It's not the smell of gas. I will try to clean behind them, but I know I won't be able to get very good access.
Any suggestions as to what that smell is exactly and why it might have just shown up recently? ...and of course, what I should do to get rid of it?