Honda Pilot 2003. I hear a sound of vibration from the engine when I drive. What could be the cause?

It does not matter what speed but of course when I'm at 30-40 mph range it is more audible. It's comes from the engine. It feels like I was driving over combed road (like the one at side of highways to wake you up). But it is not that coarse. It's a smoothers vibration than that. Its almost once every minute and stays for 5-6 seconds. Sometimes more.

Any ideas what it could be? Thanks.

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