I am newly taking over the daily operations of our warehouse facility and I've noticed that the place is filthy. A coating of black dust covers everything. I am thinking that our two trucks might be to blame. We run then on average of a couple hours a day. We asked our local service provider who came in today and he wasn't convinced. We get routine maintenance and their isn't black smoke out of the back end. Anyone else run across this kind of dust - The facility is about 60,000sqft with 22' ceilings. We do have unit heater at the ceiling - but the dust does not start when the weather turned cold - it's all year round. Any help or direction would be helpful. Thanks very much.