I'm not sure exactly what you mean by a clanking noise but I'll offer this anyway.

If you tend to mash on the pedals instead of spin, especially at your weight, you will tend to wear out chains quicker than the average cyclist. If you don't replace the chain before it gets worn too badly, you'll likely cause very quick wear of the teeth on the cassette. Eventually, when the wear gets bad enough you'll find that whenever you try to apply a lot of force that the chain slips on the cassette. This generally will only occur in the gears most often used or in the really small cogs (11 or 12 tooth).

If you are not experiencing slippage, then you likely do not have a cassette problem yet though that doesn't mean your chain isn't worn out. A worn chain, however, should not cause any clanking noises. An out-of-adjustment rear derailler is a far more likely source of noise. Deraillers go out of adjustment with use as the housing liner, pivots, and ratchets break in/wear. The fix is usually a simple adjustment to the cable tension for the rear derailler assuming the limits screws were set properly to begin with.