Socalm, this is an ongoing argument. Lay instinct says you never want to play your turntable with the dust cover closed. Then they say things like "it will sound closed in" Brilliant deductive reasoning.
As far as record care goes you never want to leave them exposed to the open environment for a prolonged period of time. Records are dust magnets. Static electricity will pull dust deep into the groove were the stylus can grind it into the vinyl, the record becomes noisier over time.
As far as sound goes, in a turntable like yours were the dust cover sits right on the same chassis as the bearing and tonearm it is possible that the cover might transmit a resonance that can be heard. In your case you do not hear a difference so it becomes a very easy choice. Now, with turntables that have an isolated chassis which the dustcover does not touch the turntable will sound better with the dust cover closed. The reason is air also transmits vibration. Putting the dust cover down is like slipping on hearing protection. It is so effective Mark Dohmann is working on an isolated dust cover for his Helix turntables.
