1998 Ford E450 Super Duty Triton V10- opinions?!

He was referring to the stabilizer bar in the rear of the unit (not stabilizer jacks). When under the RV, there is a new one in place which he noted was put on last year and upgraded to a heavier duty one so not sure why it would be clunking on each turn?! Thanks for the info on the filter and suggestions on the other possible reasons for the clunking noise (any idea on cost for repairs?). You all are a great source!