No hissing sound, but a soft "snap" instead
When I plug mine in, I can hear a soft electrical "snapping" sound when the contact is made. It's a quiet enough sound that I only hear it if there is no traffic on our street. It is about 400 watts, so imagine the sound of plugging in a 400 watt light bulb while it's turned on. I agree it would be nice to see the actual voltage at the block heater's AC input, as well as the current draw. I know I have 122 volts AC at my breaker box, but after 100' of 16/3 wire, who knows? Especially with all the salt and grime on the plug.
Lehigh Valley PA USA
73 Olds 88, 72 MB 280SE, 78 Datsun 280Z, 71 T-Bird, 72 Olds 88, 83 Nissan Sentra, 85 Sentra, 73 230.6, 91 Integra, 83 300SD, 91 Volvo 940GLE wagon, 84 300SD, 95 Subaru Legacy L wagon, 02 Mountaineer, 91 300TE, 08 Murano, 2007 R320CDI 4Matic 52K, some Hyundai, 2008 BMW 535xi wagon all gone... currently
2007 Honda Odyssey Touring, 2011 Honda Odyssey Touring