First hand from a member of the Voyager cast -
Voyager had a fairly upbeat atmosphere on set - cast 'hung out' off screen and enjoyed each others company. The cast member in question decided to visit the DS9 set on the neighbouring lot but found the staff and cast to be rather unwelcoming, keeping themselves to themselves and very little in the way of on set bonhomie. In fact he found them a thoroughly miserable bunch.
On the way back over to the Voyager lot, he met someone from the DS9 production team he knew looking agitated. When he asked what was up, he was told that someone on the DS9 crew had died in an accident on the way to work. When the Voyager cast member commented that it was no wonder the DS9 set was so miserable, he was told 'Oh, they don't know - I just was on the way to tell them !'.