We always get a musty odor when the weather is in between...not cold/not hot. The smell seems to be in only certain parts of the apartment (6 story apartment building)that you wouldn't expect. It's in the living room, in the back hall that leads to the bedroom, in the entrance way to the apartment. There's no visible evidence of mold anywhere. The apartment was renovated (new kitchen/bath/floors refinished) over the last 5 years. We recently purchased an air purifier hoping that that would solve the problem but it hasn't done much. Since it's an apartment we can't hire an engineer or have an external company come in and investigate and our building manager has come to look and says 'no signs of mold?.....no problem'. What can we do? We've even purchased those coal deodorizers. Those help a little but we would have to purchase a 100 of them for it to totally get rid of the smell every spring/fall.