Good point highflyer but they are tight. I installed the tank with good insulation around the straps as well.
It is really strange. I put some thin plastic strips between the leaves today to see if there is a difference. No. The thumping sounds so much like oil canning that it makes me wonder if it is the spring bolts. It could be telegraphing from the springs into the bed. I guess the best thing I can do now is to change the bolts and see what happens.
Golly gee, from a 737 to an A320. Bet your typing has improved! Needle, ball and airspeed is all I need. That plus a duck (IFR) and a cat (artificial horizon) and I'm all set!
