Update - Since lowering the opening height I've had no issues so far. No banging, no clumping and touch wood no failures. Spoke to the extended warranty people who say I should have further claims approved as Marshalls have already claimed for the fault. Marshalls have still not responded to me despite Merc CEO office referring to their senior management and promising me a response. Shocking from Merc and their dealers. Thanks again to everyone for your invaluable help.