As per title - after engine is thoroughly warm from a long drive of over 30 minutes I get a squeal that sounds like belt squeal, but while it is very high pitched, it is not loud.. but well concealed by the otherwise normal engine noise. It's subtle enough I thought it was tinnitus messing with me at first, but when I have the windows down rolling through the quiet residential parking lot and listen carefully, it's there, and it stops when I let off the gas or at idle. Cold start in the morning, and/or if I only do a short drive, the squeal is completely absent even under hard acceleration and with the AC on. Checked the basics - no wobble of serpentine belt on pulleys, no wobble of pulleys themselves, none seized, no grinding noises and belt tension feels within spec. Engine has a timing chain rather than timing belt. Don't have any means of loosening the tensioner myself so I can't remove the belt to hand-spin the pulleys - will have to get that checked at the shop. Is there something obvious I should know if I get a squeal only after thoroughly warmed and driven a bit? My past experiences with belt squeals is that they are worse in the morning or when it is wet.. so this one seems totally out of whack. Maybe it's not even the belt..?