It was no surprise to find the rattling or clunking from the bonnet on my Plus 4 but on inspection I found that the position of bonnet rubber meant it was not anywhere near the surface of each side when closed. My solution was to get two additional rubbers and a pair of plastic spacers from a wall mounted TV kit and reassemble these so that each rubber was mated to its partner and a spacer allowed me ensure that the combination actually allowed each bonnet side to rest securely once it was closed by the latches on each side.
Next step was to grease the flat strips at front and rear and add a few neoprene drawer bumpers from kitchen DIY. Definitely a big improvement.
I put candle wax on my bonnet support strips. Grease attracts muck and leaves an awful mess. Remember the fixed bonnet catches have slots to allow up and down movement, in turn offering bonnet seating adjustment.
