It could be foaming, the plane vibrates alot at certain speeds including low idle. I do have foam around the engines but not alot because of the tight fit. As for idling on engine, I have the gear and spoiler pots mixed out on the outer engines but I can mix them back in so I can control them independently of the center engine. Sounds like I need to do it. If I have altitude, I have no problem cutting everything down and making a deadstcik landing but engines don't always cut out at altitude!

Jeff