Offshoreonly.com - 525efi's Lifter issues???

I have 2 ea. Merc. 525efi's that have 100 hours on them. Boat set in dry storage for 3 months but was started every month. In early March, I went to warm the oil prior to changing it. Both motors had immediate lifter knock noise when I started them. One cleared after about 30 seconds, the other took about 5 minutes and then they ran great. I changed the oil, restarted, and was fine. 2 weeks later, I started boat and both engines had lifter knock noise. Again, 1 cleared in about 3 minutes and the other didn't clear for about 15 minutes and had a mild "pop" sounding like it was through the intake. They cleared and ran great. Let it set for 4 days, started and no problems. Let it set for 2 more days and was identical to last incident where 1 took about 15 minutes to clear after running it (then ran it for 8 hours at 4000 rpm's with no problems). Sounds to me like lifters are having issues pumping up. Have used same oil since new and am original owner - late 2005 motors. Can lifters have leak down issues and then run great after pumping up? Merc. states no issues to date. Any thoughts from the OSO group? Thanks - TH