I've read thru the posts on this subject that I could locate here in S.L., and listened to ours today while out for 3.5 hours with start and stop at multiple times along the way. initial start after sitting for a few days, Cold drinks at rest stops, bathroom break, ice cream stop, and gas on way home. 160 miles total. My main conclusion (opinion) is that the noise only occurred at the initial start-up. It was not noticeable (to me) at any of the follow-on shutdown/startups. I am thinking it is merely the system being replenished with oil after the drain back we are all familiar with based on the oil level test procedure. Sitting for "some period" will cause it (overnight?), while shorter times between shutdown and startup won't. All of this of course is IMHO. Any more thoughts on this issue from others?