Bloom Energy makes fuel cells that can run on natural gas. This site would need a very large number of them to replace gas generators. Each "bloom box" can create 325kW and are about 1m x 1m x 2m in size.

They make sort of whine/squeal noise when operating. Not sure of the dB level.

San Jose Ice Rink has had a bunch of these installed out back for about 10 years I think.

Well, most of the results on google images for "natural gas fuel cell" are of renderings or diagrams instead of actual equipment, that sould say something. Probably that they arent very common.