What is causing a slight vibration in my drivetrain when accelerating.

99 Honda Accord V6, this started about two weeks ago while driving home from work. Stopped a a light when I took off felt like a (difficult to explain) "tuc tuc tuc". Not audible to the ear but felt it like on the drive train, when I let go off the accelelator it would subside. Next morning did not feel anything everything was normal until I drove 14 miles and it started again. It never starts right away when the car is cold, only after driving 15-18 miles and it feels worse when I hit the gas subsides when coasting.
The car has original drive axles & hub bearings, after a visual inspection on jacks this past weekend all the boots amazingly good not cracked. Attaching bolts and nuts seemed tight and in place. As far as end play I don't know what to look for on the axles. Visually everything looks fine on the suspension components.
Engine mounts are also original except for the side mount, I also checked them with my wife in the drivers seat and me under the hood, going into drive and reverse, you know the drill!
Wheels are Michelins with only 5K miles on it. No warning lights of any kind have been on. I highly suspect my drive axles but don't know how to check. I had this car since it had 21K miles and has been great, no previous accidents and even the paint still shines. Any suggestions in where to star looking? Have you seen this problem before. Please advice. Thanks in advance.

Best Regards
Tony