As Sean stated, if the guides are in good condition and it doesn't rattle, especially on the first 30 seconds of a cold start, leave it alone.
If you have a slight rattle on a cold start for no more than a few seconds (10-15) there is a good chance the tensioner is sticking with age, replace the tensioner period as soon as you can as it will only get worse. If this doesn't stop the rattle then your up for new guides as a minimum.
Once the rattle becomes more pronounced, your starting to damage your guides !
If the rattle doesn't go away, stop running the engine period ! pull the valve cover and inspect the guides, your going to find your up for new guides and tensioner and will need a specific tool to hold the cam in position to remove the sprocket to replace the guides (you would have already removed the tensioner for obvious reasons).
If your replacing the timing chain, your also replacing the cam sprocket and crank sprocket. The hard part is to replace the crank sprocket as you need to heat it up to 150C (no more) and install it and allow it to cool (heat shrink) so your looking at a very big job.
Another consideration when your tensioner sticks and the chain starts slapping around is that it will damage your oil pump housing which is part of the timing chain cover !
If you only replace the timing chain, it wont last as long due to wear on the sprockets that may not be as obvious as you think so to do the job correctly your looking at dropping the engine out and for all purposes, rebuilding it as your going to be pulling the crankshaft out.
Look on YouTube for Modmini, he has a video on replacing the timing chain guides. he also covers damage to the timing chain cover (oil pump), he has a series where he rebuilds a blown motor and this shows you how the timing chain is correctly set to the cam and crank sprocket to maintain correct valve timing (chain has bright links and both sprockets have alignment marks).
The good news is, a sticking tensioner is a quick and easy fix, a little more of a fiddle on an R53 than an R50 due to the oil heat exchanger getting in the way.
The bad news is, if you need to replace the guides, you need to buy the cam locking tool but with a Bentley manual, the right tools and watch Modmini's video several times to get to grips with the work flow, its about a 2-3 hour job the 1st time you do it and is an easy DIY for those with a bit of mechanical knowledge.
To save skinned knuckles and rounded bolts, I highly recommend you take the heat exchanger off and while your at it, replace the 2 O-rings in it (R53 models) as it allows you easy access to the tensioner and the ability to correctly torque it up once replaced.
I have attached some files for you to look at on top of having a manual and watching the Modmini videos created from when I had to replace my R53 tensioner and timing chain guides.
One of the top tips from Modmini when you remove the Cam sprocket is to use either liquid paper or whit paint to mark its exact tooth location to the timing chain, and suspend the chain under tension so that it doesn't loose its position on the crank sprocket. If you find bits of guide have vanished, your also looking at dropping the sump to clean out the debris and therefore a complete oil change with oil filter.