This doesn't sound like normal operation. Maybe a buzz or a click when anything electrical starts up can be considered normal, but if it's noisy - or noisy-"ER", you might want to have the unit inspected. You can set that up online, or by calling 800-SAMSUNG.
I notice occasionally a whirring sort of sound almost like a drive or CD spinning up but rather noisily when I first turn on my set. I just got this set a few weeks ago and don't recall it doing it initially. Anyone experience this? After a few seconds it seems fine.