Lifter tapping when cold after full synthetic oil change high mileage Nissan maxima.?

295K miles, that's awesome. You must really take good care of your vehicles. You most likely have a lifter that is sticking or gummed up and not pumping up. This may sound strange, but it has worked for me in the past. Try and drain out a quart and then add one quart of Mobil one syn transmission oil. Transmission oil has a lot of detergent type additives and is also lighter weight. Run this for awhile and I bet your lifter will clean out.